Silicone rubber composition

Abstract

The present disclosure relates to a silicone-based composition comprising one or more non-fluorinated polydiorganosiloxane polymers and a silica filler, the silica filler being at least partially treated with a fluorinated hydrophobizing treatment, a method for preparing the composition, and its use in the manufacture of insulators for high voltage applications, particularly high voltage direct current (HVDC) applications, as well as accessories such as cable joints, cable terminations, and connectors. The treatment is selected from one or more silanol-terminated fluorinated siloxane oligomers having 2 to 20 siloxane units, one or more fluorinated silanediols, one or more fluorinated trialkoxysilanes, and / or one or more fluorinated silazanes, or mixtures thereof.

Description

[Technical Field]

[0001] The present disclosure relates to silicone-based compositions comprising one or more non-fluorinated polydiorganosiloxane polymers and a silica filler, wherein the silica filler has been at least partially treated with a fluorinated hydrophobizing agent, to a method for their preparation, and to their use in the manufacture of insulators for high voltage applications, particularly high voltage direct current (HVDC) applications, and in the manufacture of accessories such as cable joints, cable termination applications, and connectors.

[0002] While alternating current (AC) is often preferred for delivering electricity to end users, long-distance transmission, e.g., distances >1000 km, can be accomplished using high-voltage direct current (HVDC) systems because HVDC systems have fewer electrical losses and are therefore less expensive. Long-distance HVDC transmission is generally accomplished through three methods: overhead (e.g., via pylons); underground systems; and, if necessary, "subsea" systems, such as undersea transport. It can be argued that underground systems are significantly more aesthetically pleasing to the public than pylons, while the latter may be perceived as more practical but unsightly. However, underground HVDC transmission generally presents the greatest challenge for suppliers compared to overhead and subsea systems, as it involves the use of multiple lengths of cable that are interconnected through cable joints every 1–2 km. Therefore, while cable joints are required for all types of HVDC transmission, this requirement is particularly acute for underground systems.

[0003] However, insulating materials utilized for AC current transmission systems cannot always be transferred to DC transmission systems, since electrical stresses differ significantly between AC and DC conditions, particularly since, under DC conditions, insulating materials are subjected to higher and continuous electrical stresses that may cause breakdown of the material. Addressing such issues is particularly important today, given the ever-increasing HVDC voltage requirements for new cables and cable accessories, which can now be >500 kV or even >800 kV.

[0004] In DC transmission, power cable systems have a resistive electric field distribution that depends on the volume resistivity. In contrast to joints used in high voltage AC applications, it is important to minimize any difference in dielectric constant between the cable insulation and the joint insulation to obtain the desired performance.

[0005] Thus, in HVDC systems, for example, in joint boxes for HVDC power cables, the cable is surrounded by an inner layer of "cable insulation," which may be made from a suitable material such as cross-linked polyethylene (XLPE), and the cable insulation is surrounded by a further layer of insulation, typically referred to as "joint insulation," often provided in the form of ethylene propylene diene monomer rubber (EPDM) or silicone rubber elastomer material. Therefore, in high-voltage direct current applications, it is important to minimize any difference in volume resistivity between the cable insulation and the joint insulation to ensure a uniform distribution of the electric field at their interface, e.g., to avoid dielectric breakdown. Therefore, it is desirable to design the joint insulation material and the cable insulation material to have volume resistivity values ​​as close to each other as possible.

[0006] The current approach of using a combination of cross-linked polyethylene (XLPE) as the cable insulation and a silicone rubber-based elastomer material as the joint insulation faces stability issues due to the difference in their electrical properties. Typically, unmodified silicone rubber-based elastomer materials are too insulating compared to XLPE under the same electric field strength. Silicone rubber-based materials, once cured into the final product, are excellent electrical insulators, typically exceeding (≥) 10, depending on the sample preparation and measurement method. 15 It has a volume resistivity of less than ohm-cm, which is much greater than the typical volume resistivity of XLPE.

[0007] Historically, the industry solution has been to introduce conductive fillers (e.g., metal powders, metal flakes, carbon black, or carbon nanotubes) or semi-conductive fillers into silicone rubber compositions to improve the performance of silicone rubber elastomer materials made therefrom. 10 ~10 15 ohm-cm, or 10 10 ~10 14 The goal was to make it sufficiently conductive to allow for localized DC load distribution through a slightly conductive silicone elastomer product made with a conductive LSR composition that provides bulk resistivity in the ohm-cm range.

[0008] However, although the use of these conductive and / or semiconductive fillers can solve the local DC load distribution, the introduction of such fillers can sometimes cause further problems, in particular the inability to control and / or obtain uniform electrical properties within the silicone elastomer, resulting in poor physical properties and reduced dielectric strength.

[0009] Recently, it has been discovered that an elastomeric material made from a composition comprising a mixture of fluorinated and non-fluorinated polydiorganosiloxane polymers, prepared by blending a fluorinated polydiorganosiloxane polymer base with a non-fluorinated polydiorganosiloxane polymer base, each base comprising a polymer and a reinforcing filler, can provide an insulating material with a volume resistivity approaching that of crosslinked polyethylene without the need for conductive or semiconductive fillers. However, while the use of such mixtures represents a significant improvement over the use of compositions using only conductively filled non-fluorinated polydiorganosiloxane polymers, they have the potential drawback of being significantly more expensive to produce, because the physical properties of the resulting elastomers can deteriorate with the weight percent (wt%) of fluorinated polydiorganosiloxane polymer in the polymer, and because blends of fluorinated and non-fluorinated polydiorganosiloxane polymers can phase separate, requiring the use of compatibilizers.

[0010] Therefore, there remains a need to develop silicone rubber insulating materials that can withstand the high electrical stresses imposed on cable insulation and cable joint insulation in high voltage direct current (HVDC) and high voltage alternating current (HVAC) systems. For HVDC systems, it is desirable to provide silicone-based insulation with electrical properties that match the range of XLPE volume resistivity values, which may be advantageous for applications in high voltage direct current (HVDC), such as cables and cable joints.

[0011] It has been found that the need to utilize either elastomers comprising a mixture of fluorinated and non-fluorinated polydiorganosiloxane polymers, or silicone rubber compositions containing conductive and / or semi-conductive fillers, can be avoided by using one or more non-fluorinated polydiorganosiloxane polymers in conjunction with a finely divided reinforcing silica filler that has been at least partially treated with a fluorinated hydrophobizing agent.

[0012] 1. A curable silicone elastomer composition comprising: (A) at least one non-fluorinated polydiorganosiloxane; (B) at least one reinforcing silica filler that has been at least partially hydrophobized with a fluorinated hydrophobizing agent, the fluorinated hydrophobizing agent being: one or more silanol-terminated fluorinated siloxane oligomers having 2 to 20 siloxane units, and / or one or more fluorinated silanediols, and / or one or more fluorinated trialkoxysilanes, and / or one or more fluorinated silazanes, or mixtures thereof; at least one reinforcing silica filler selected from At least one of (C) or (D); Including, (C) is at least one organohydrogenpolysiloxane (C)(i), at least one hydrosilylation catalyst (C)(ii), and optionally at least one cure inhibitor (C)(iii); and Compositions are provided in which (D) is at least one peroxide catalyst.

[0013] In addition, the curable silicone elastomer composition Use in or as a high voltage direct current insulator, comprising: (A) at least one non-fluorinated polydiorganosiloxane; (B) at least one reinforcing silica filler that has been at least partially hydrophobized with a fluorinated hydrophobizing agent, the fluorinated hydrophobizing agent being: one or more silanol-terminated fluorinated siloxane oligomers having 2 to 20 siloxane units, and / or one or more fluorinated silanediols, and / or one or more fluorinated trialkoxysilanes, and / or one or more fluorinated silazanes, or mixtures thereof; at least one reinforcing silica filler selected from At least one of (C) or (D); Including, (C) is at least one organohydrogenpolysiloxane (C)(i), at least one hydrosilylation catalyst (C)(ii), and optionally at least one cure inhibitor (C)(iii); and There is also provided a use of the composition, wherein (D) is at least one peroxide catalyst.

[0014] Also provided is a high voltage DC insulator comprising an elastomeric product of a curable silicone elastomer composition, the composition comprising: (A) at least one non-fluorinated polydiorganosiloxane; (B) at least one reinforcing silica filler that has been at least partially hydrophobized with a fluorinated hydrophobizing agent, the fluorinated hydrophobizing agent being: one or more silanol-terminated fluorinated siloxane oligomers having 2 to 20 siloxane units, and / or one or more fluorinated silanediols, and / or one or more fluorinated trialkoxysilanes, and / or one or more fluorinated silazanes, or mixtures thereof; at least one reinforcing silica filler selected from At least one of (C) or (D); Including, (C) is at least one organohydrogenpolysiloxane (C)(i), at least one hydrosilylation catalyst (C)(ii), and optionally at least one cure inhibitor (C)(iii); and Also provided is a high voltage DC insulator wherein (D) is at least one peroxide catalyst.

[0015] In yet a further embodiment, there is provided a high voltage direct current insulator comprising an elastomeric product obtained or obtainable by curing a curable silicone elastomer composition, the composition comprising: (A) at least one non-fluorinated polydiorganosiloxane; (B) at least one reinforcing silica filler that has been at least partially hydrophobized with a fluorinated hydrophobizing agent, the fluorinated hydrophobizing agent being: one or more silanol-terminated fluorinated siloxane oligomers having 2 to 20 siloxane units, and / or one or more fluorinated silanediols, and / or one or more fluorinated trialkoxysilanes, and / or one or more fluorinated silazanes, or mixtures thereof; at least one reinforcing silica filler selected from At least one of (C) or (D); Including, (C) is at least one organohydrogenpolysiloxane (C)(i), at least one hydrosilylation catalyst (C)(ii), and optionally at least one cure inhibitor (C)(iii); and A high voltage direct current insulator is provided in which (D) is at least one peroxide catalyst.

[0016] Also disclosed is a method for preparing a curable silicone elastomer composition, the composition comprising: (A) at least one non-fluorinated polydiorganosiloxane; (B) at least one reinforcing silica filler that has been at least partially hydrophobized with a fluorinated hydrophobizing agent, the fluorinated hydrophobizing agent being: one or more silanol-terminated fluorinated siloxane oligomers having 2 to 20 siloxane units, and / or one or more fluorinated silanediols, and / or one or more fluorinated trialkoxysilanes, and / or one or more fluorinated silazanes, or mixtures thereof; at least one reinforcing silica filler selected from (C) and optionally at least one of (D); Including, (C) is a hydrosilylation cure package comprising at least one organohydrogenpolysiloxane (C)(i), at least one hydrosilylation catalyst (C)(ii), and optionally at least one cure inhibitor (C)(iii); and (D) is at least one peroxide catalyst, and the process comprises: (i) preparing a silicone-based composition by mixing a non-fluorinated polydiorganosiloxane (A) with at least one reinforcing silica filler; (ii) introducing component (C), or a mixture of component (C) and component (D), and storing the resulting composition, wherein if the composition contains a hydrosilylation cure package (C), the composition is stored in two or more parts in which components (C)(i) and (C)(ii) are maintained in separate parts; Also provided is a method wherein the at least one reinforcing silica filler is at least partially treated with a fluorination treating agent prior to or during step (i).

[0017] The compositions described herein above do not include fluorinated polydiorganosiloxane polymers having more than (>) 20 repeating siloxane units that contain silanol groups.

[0018] For purposes of this application, the term "free" shall be understood to mean free of fluorinated polydiorganosiloxane other than trace amounts of impurities and residual unreacted filler treating agent.

[0019] Preferably, the composition contains no more than (≦) 0.1% by weight of the composition of conductive or semi-conductive fillers or mixtures thereof, and in one embodiment, the composition contains 0 (zero)% by weight of conductive or semi-conductive fillers.

[0020] (C) When a hydrosilylation cure package is present in the composition, the non-fluorinated polydiorganosiloxane (A) will contain at least one, alternatively at least two, unsaturated groups, e.g., alkenyl or alkynyl groups, per molecule. However, when component (D) is the sole means of catalysis for the cure process, it is preferred, but not required, that component (A) have at least one alkenyl or alkynyl group per molecule, or at least two alkenyl or alkynyl groups per molecule.

[0021] For purposes of this application, "substituted" means that one or more hydrogen atoms in a hydrocarbon group have been replaced with another substituent. Examples of such substituents include, but are not limited to, halogen atoms such as chlorine, bromine, and iodine; halogen-containing groups (other than fluoro) such as chloromethyl; oxygen atoms; oxygen-containing groups such as (meth)acrylic groups and carboxyl groups; nitrogen atoms; nitrogen-containing groups such as amino, amide, and cyano functional groups; sulfur atoms; and sulfur-containing groups such as mercapto groups.

[0022] The present specification provides a silicone rubber composition containing a non-fluorinated silicone polymer and a reinforcing silica filler, wherein at least a portion of the silica is treated with a fluorinated hydrophobizing agent, and the fluorinated hydrophobizing agent is one or more silanol-terminated fluorinated siloxane oligomers having 2 to 20 siloxane units, and / or one or more fluorinated silanediols, and / or one or more fluorinated trialkoxysilanes, and / or one or more fluorinated silazanes, or mixtures thereof The composition is selected from It has been found that the modified silica treatment using the fluorination treating agent exhibits greater effectiveness in changing the electrical properties of the silicone rubber into a conductivity range consistent with the desired XLPE volume resistivity value. The modified silica treatment using the fluorination treating agent acts to reduce the volume resistivity of the silicone rubber to up to 60% of the volume resistivity of an equivalent silicone rubber prepared without the modified silica treatment, a desired target range equivalent to the typical volume resistivity of XLPE materials used as cable insulation. Surprisingly, it has been found that the use of silica at least partially treated with the fluorination treating agent can potentially be used in combination with different silicone rubbers, such as liquid silicone rubber (LSR) and high viscosity rubber (HCR), to target the electrical properties of these materials into a desired range by varying the content of the fluorination treating agent-treated silica within the range of treated silica required for the composition.

[0023] Surprisingly, it has been found that when the content of the fluorinated treating agent-treated silica is varied within the amount of treated silica in the composition, neither fluorinated polydiorganosiloxane polymers nor conductive or semiconductive fillers are required in the silicone rubber compositions herein to obtain a silicone elastomer with the desired volume resistivity. It has also been shown that available silicone rubber formulations can include liquid silicone rubber compositions or high-viscosity silicone rubber-based materials that utilize polydiorganosiloxane polymer gums. By using the fluorinated treating agent-treated silica as the only fluorinated portion of the composition, it has been found that a wide range of volume resistivities can be efficiently accessed simply by varying the loading of the fluorinated treating agent-treated silica, as shown in the examples. This has the advantage of being much more economical than previous solutions and avoiding the types of problems encountered with previous solutions to this problem, such as the compatibility issues already mentioned.

[0024] The non-fluorinated polydiorganosiloxane polymer (A) has the formula (I): R a SiO (4-a) / 2 (I) wherein each R is independently selected from an aliphatic hydrocarbyl group, an aromatic hydrocarbyl group, or an organyl group (i.e., any organic substituent having one free valence at a carbon atom, regardless of the type of functional group). Examples of saturated aliphatic hydrocarbyls include, but are not limited to, alkyl groups such as methyl, ethyl, propyl, pentyl, octyl, undecyl, and octadecyl, and cycloalkyl groups such as cyclohexyl. Examples of unsaturated aliphatic hydrocarbyls include, but are not limited to, alkenyl groups such as vinyl, allyl, butenyl, pentenyl, cyclohexenyl, and hexenyl, and alkynyl groups. Examples of aromatic hydrocarbon groups include, but are not limited to, phenyl, tolyl, xylyl, benzyl, styryl, and 2-phenylethyl. Examples of organyl groups include, but are not limited to, halogenated alkyl groups (excluding fluoro-containing groups) such as chloromethyl and 3-chloropropyl, nitrogen-containing groups such as amino, amido, imino, and imido groups, and oxygen-containing groups such as polyoxyalkylene, carbonyl, alkoxy, and hydroxyl groups. Additional organyl groups can include sulfur-, phosphorus-, and boron-containing groups. The subscript "a" is 0, 1, 2, or 3.

[0025] Siloxy units may be described by the contractions (abbreviations) "M," "D," "T," and "Q" when R is a methyl group (further teachings on silicone nomenclature can be found in Walter Noll, Chemistry and Technology of Silicones, dated 1962, Chapter I, pages 1-9). M units are siloxy units where a=3, i.e., RSiO 1 / 2 and the D units are siloxy units where a=2, i.e., RSiO 2 / 2 and T units are siloxy units where a=1, i.e., RSiO 3 / 2 and the Q units are siloxy units where a=0, i.e., SiO 4 / 2 is equivalent to

[0026] Typical examples of groups in the non-fluorinated polydiorganosiloxane polymer (A) include primarily alkenyl, alkyl, and / or aryl groups. The groups may be pendant (on D or T siloxy units) or terminal (on M siloxy units). As mentioned above, alkenyl and / or alkynyl groups are essential when component (C) is involved in the curing process, but are optional when component (D) is the sole catalyst for the curing process. Thus, when present, suitable alkenyl groups in component (A) typically contain 2 to 10 carbon atoms, with preferred examples being vinyl, isopropenyl, allyl, and 5-hexenyl.

[0027] The silicon-bonded organic groups attached to component (A) other than alkenyl groups are typically selected from monovalent saturated hydrocarbon groups containing 1 to 10 carbon atoms and monovalent aromatic hydrocarbon groups typically containing 6 to 12 carbon atoms, which are unsubstituted or substituted with groups that do not interfere with the cure of the compositions of the present invention, such as halogen atoms. Preferred species of silicon-bonded organic groups are alkyl groups such as methyl, ethyl, and propyl, and aryl groups such as phenyl.

[0028] The non-fluorinated polydiorganosiloxane polymer may be selected from, for example, polydimethylsiloxane, alkylmethylpolysiloxane, alkylarylpolysiloxane, or copolymers thereof containing alkenyl and / or alkynyl groups (reference to alkyl means alkyl groups having two or more carbons), and may have any suitable end groups, such as trialkyl-terminated, alkenyldialkyl-terminated, alkynyldialkyl-terminated, or any other suitable combination of end groups, provided that each polymer contains at least two unsaturated groups selected from alkenyl and alkynyl groups per molecule. Preferably, the end groups of such polymers have less than (<) 10 wt.% or no silanol end groups. Thus, the non-fluorinated polydiorganosiloxane polymer may be, for example, a dimethylvinyl-terminated polydimethylsiloxane, a dimethylvinylsiloxy-terminated dimethylmethylphenylsiloxane, a trialkyl-terminated dimethylmethylvinylpolysiloxane, or a dialkylvinyl-terminated dimethylmethylvinylpolysiloxane copolymer.

[0029] The molecular structure of component (A) is typically linear, although some branching may be present due to the presence of T units (as described above) within the molecule. To achieve useful levels of physical properties in the elastomers prepared by curing the compositions as described above, the molecular weight of component (A) should be sufficient to achieve a viscosity of at least 1000 mPa·s at 25°C using the cup / spindle method of ASTM D 1084 Method B, using the most appropriate spindle in the Brookfield® RV or LV range for that viscosity range. The upper molecular weight of component (A) is not particularly restricted and is typically limited only by the processability of the LSR compositions of the present invention.

[0030] However, (A) can also be a gum. Polydiorganosiloxane gums typically have a viscosity of at least 1,000,000 mPa·s at 25°C. However, because measuring viscosities above these values ​​is difficult, gums tend to be described by their Williams plasticity value according to ASTM D-926-08 rather than viscosity. Thus, polydiorganosiloxane gum (A) has a viscosity resulting in a Williams plasticity of at least 30 mm / 100 as measured according to ASTM D-926-08, alternatively at least 50 mm / 100 as measured according to ASTM D-926-08, alternatively at least 100 mm / 100 as measured according to ASTM D-926-08, alternatively between 100 mm / 100 and 300 mm / 100 as measured according to ASTM D-926-08.

[0031] An example of component (A) is a polydiorganosiloxane containing two terminal alkenyl groups and is represented by the general formula (II): R'R''R'''SiO-(R''R'''SiO) m -SiR'''R''R'(II)

[0032] In formula (II), each R' is an alkenyl group, typically containing from 2 to 10 carbon atoms, such as vinyl, allyl, and 5-hexenyl.

[0033] 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 that do not interfere with the cure of the compositions of the present invention, such as halogen (except fluorine) atoms. R'" is R' or R". For the avoidance of doubt, none of the R'", R', or R" groups in the component (A) polymer may contain fluoro groups or any fluorine-containing groups. As noted above, when the polymer is designed to be used as part of an LSR composition, the letter m represents a degree of polymerization suitable for component (A) to have a viscosity of 1,000 mPa·s to 100,000 mPa·s at 25°C by ASTM D 1084 Method B cup / spindle method, using the most appropriate Brookfield® RV or LV range spindle for the viscosity range. However, if (A) is in the form of a gum, its viscosity will be >1,000,000 mPa.s at 25°C, often significantly >1,000,000 mPa.s at 25°C, resulting in a significantly larger value of m and a Williams plasticity measurement rather than viscosity.

[0034] The alkenyl and alkynyl groups of polymer (A) are determined using quantitative infrared analysis according to ASTM E168.

[0035] (B) Reinforcing silica filler Component B is a reinforcing silica filler that has been at least partially hydrophobically treated with the fluorination treating agent to achieve the high level of physical properties that characterize some types of cured silicone elastomers that can be prepared using the compositions herein, providing a reinforcing silica filler (B), such as a finely divided silica filler that has been at least partially hydrophobically treated with the fluorination treating agent.

[0036] The finely divided form of silica may be selected from, for example, fumed silica, precipitated silica, and / or colloidal silica. They are typically at least 50 ml2 This is particularly preferred because it has a relatively large surface area of ​​100 to 600 m / g measured according to the BET method. 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 ​​0.01g / g (using the BET method according to ISO 9277:2010) are typically used.

[0037] When component B, the reinforcing silica filler, is naturally hydrophilic (e.g., untreated silica filler), it is often surface treated with one or more known filler treating agents to prevent a phenomenon called "creping" or "crepe hardening" during processing of the curable composition.

[0038] The reinforcing silica filler may be treated either prior to introduction into the composition or in situ (i.e., by blending these components together in the presence of at least some of the other components of the composition described above until the filler is completely surface treated and uniformly dispersed to form a homogeneous material). In one embodiment, untreated filler (B) is treated in situ with a treating agent in the presence of component (A).

[0039] In the present composition, the reinforcing silica filler (B) is The surface is at least partially treated with a fluorinated hydrophobic treatment agent, and the fluorinated hydrophobic treatment agent is one or more silanol-terminated fluorinated siloxane oligomers having 2 to 20 siloxane units, and / or one or more fluorinated silanediols, and / or one or more fluorinated trialkoxysilanes, and / or one or more fluorinated silazanes, or mixtures thereof is selected from.

[0040] The fluorination treatment agent is It may include a silanol-terminated fluorinated siloxane oligomer containing 2 to 20 siloxane units having the formula: (R 2 Z) d (R 3 ) e SiO (4-d-e) / 2 [In the formula, Each R 2 may be the same or different and represent a branched or linear fluoroalkyl group having 1 to 8 carbon atoms, Each Z may be the same or different and represents a divalent alkylene group containing at least two carbon atoms, a hydrocarbon ether, or a hydrocarbon thioether; 2 The group is linked to the silicon atom via the Z group, Each R 3 groups are the same or different and represent alkyl groups having 1 to 10 carbon atoms; d may be 1 to 3, e may be 0 to 3, and (d+e) is 1 to 3.

[0041] Preferred saturation R 3 Exemplary groups include alkyl groups such as methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl, hexyl, 2-ethylhexyl, octyl, isooctyl, and decyl, or those having 1 to 6 carbons, or methyl, ethyl, propyl, isopropyl, n-butyl, or t-butyl, or methyl or ethyl, or methyl;

[0042] Preferably, R 2 R represents a fluoroalkyl group having at least one carbon atom, alternatively 1 to 8 carbon atoms, over the entire range of 5 to 100 mole percent of fluorinated siloxane units. Each fluoroalkyl group present has at least one —CF bond. 2The groups may be the same or different and may have a normal or branched structure. Preferably, at least some of the fluoroalkyl groups, most preferably more than 50%, are perfluoroalkyl groups. Examples include CF3-, C2F5-, C3F7-, such as CF3CF2CF2- or (CF3)2CF-, C4F9-, such as CF3CF2CF2CF2-, (CF3)2CFCF2-, (CF3)3C- and CF3CF2(CF3)CF-; C5F 11 , e.g., CF3CF2CF2CF2CF2-, CF 13 -, e.g., CF3(CF2)4CF2-; C7F 14 -, for example CF3(CF2CF2)3-; and C8F 17 Examples include:

[0043] Each perfluoroalkyl group is attached to the silicon atom by Z, a divalent spacing group containing carbon, hydrogen, and optionally oxygen and / or sulfur atoms present as ether and thioether linkages, respectively. The sulfur and oxygen atoms, when present, shall be attached only to carbon atoms.

[0044] Each Z group can have any structure containing the listed elements, but is preferably an alkylene group (i.e., an acyclic, branched, or unbranched saturated divalent hydrocarbon group). Examples of suitable alkylene groups include -CH2CH2-, -CH2CH2CH2-, -CH(CH3)CH2-, (CH2CH2)2-, and -CH(CH3)CH2CH2-. In one embodiment, each fluorinated group R 2 Z is preferably of the formula R 2 It has CH2CH2-, i.e., Z is an ethylene group.

[0045] As mentioned above, d may be 1 to 3, e may be 0 to 3, and (d+e) is 1 to 3, or (d+e) is 2 or 3, or (d+e) is 2, d=1 and e=1. Preferably, when e is >0, R 3At least 90 percent, and more preferably all, of the groups are methyl groups.

[0046] The fluorinated siloxane oligomer may further comprise up to about 90%, alternatively up to about 80%, of the total number of units per molecule of non-fluorinated siloxane units having the following formula: (R 4 ) c SiO (4-c) / 2 [In the formula, R 4 represents an optionally substituted saturated or unsaturated silicon-bonded monovalent hydrocarbon radical, where c=0 to 3, preferably with an average value of about 2. 4 does not contain fluorine (hence, R 4 may not contain any of the previously specified fluoro-containing substituents.

[0047] As mentioned above, R 4 represents an optionally substituted saturated or unsaturated silicon-bonded monovalent hydrocarbon radical. Preferably, each R 4 may be the same or different, C1 to C 10 Alkyl groups, such as vinyl or allyl groups, and / or aryl groups, such as phenyl, tolyl, benzyl, β-phenylethyl, and styryl, where each alkenyl group, if present, has from 2 to 8 carbon atoms, alternatively each alkenyl group is a vinyl group.

[0048] Fluorinated siloxane oligomers having 2 to 20 siloxane units can be illustrated by the following formula: HO-[(R 2 Z) d (R 3 ) e Si-O] f -H (In the formula, R 2 , Z, d, R 3 , and e are as defined above, and f is 2 to 20).

[0049] Fluorinated silanediols can be illustrated by the following formula: (HO)2Si(R 2 Z)(R 3 ) (In the formula, R 2 , Z, and R 3 are as defined above).

[0050] Fluorinated trialkoxysilanes can be illustrated by the following formula: R 2 Z-Si(R g )3 (In the formula, R 2 is as defined above, and each R g may be the same or different and are an alkoxy group having 1 to 6 carbons, or an alkoxy group having 1 to 4 carbons, or a t-butoxy, ethoxy, or methoxy group).

[0051] Fluorinated silazanes can be illustrated by the following formula: ((R 2 Z)(R 3 )2-Si)2-NH (In the formula, R 2 , Z, and R 3 and each are as defined above). In one alternative, each R 3 has 1 to 6 carbons, alternatively 1 to 3 carbons, or is ethyl or methyl.

[0052] The fluorination treatment agent may be selected from the group consisting of trifluoropropyltrialkoxysilanes, such as trifluoropropyltrimethoxysilane and trifluoropropyltriethoxysilane; silanol-terminated trifluoropropylalkylsiloxanes having 2 to 20 siloxane repeat units and in which the alkyl group has 1 to 6 carbons, such as silanol-terminated trifluoropropylmethylsiloxanes having 2 to 20 siloxane repeat units and silanol-terminated trifluoropropylethylsiloxanes having 2 to 20 siloxane repeat units, and bis(trifluoropropyldialkyl)silazanes in which each alkyl group has 1 to 6 carbons, alternatively 1 to 3 carbons, or is a methyl or ethyl group.

[0053] Although the treating agents are primarily used to render the filler hydrophobic, thereby facilitating handling and allowing a homogeneous mixture with the other ingredients, it has been found herein that, as noted above, by varying the amount of reinforcing filler treated with one or more of the above fluorinated treating agents, the volume resistivity of the resulting elastomeric material can be varied.

[0054] The remainder of the reinforcing silica (B), if present, is treated with a non-fluorinated hydrophobizing agent, such as, for example, an organosilane, polydiorganosiloxane, or organosilazane, hexaalkyldisilazane, short-chain siloxanediol, fatty acid or fatty acid ester, e.g., stearates, all of which are non-fluorinated. Again, this renders the remaining reinforcing silica (B) filler hydrophobic, thereby facilitating handling and achieving a homogeneous mixture with the other ingredients. Specific examples include, but are not limited to, non-fluorinated liquid hydroxyl-terminated polydiorganosiloxanes containing an average of 2 to 20 diorganosiloxane repeat units, hexaorganodisiloxanes, hexaorganodisilazanes, and the like.

[0055] In either case, a small amount of water or ammonium hydroxide may be added as a processing aid along with the silica treating agent. The surface treatment of the filler allows it to be easily wetted by the polymer of component (A). These surface-modified fillers do not agglomerate and can be homogeneously incorporated into component (A), resulting in improved mechanical properties of the uncured composition at room temperature.

[0056] The amount of silica reinforcing filler used in the compositions described herein is typically about 1-40 weight percent (wt%) of the composition, alternatively 5-35 wt% of the composition, alternatively 10-35 wt% of the composition, alternatively 15-35 wt% of the composition. Treating agents utilized are typically added in an amount of 1-10 wt% of the total composition (i.e., after mixing Parts A and B if stored as a multi-part composition), alternatively 1-10 wt% of the total composition.

[0057] In one embodiment, at least 20 wt.% of the total silica surface is treated with a fluorinated hydrophobizing agent. This fluorinated hydrophobizing agent may be uniformly distributed over the entire silica surface when a mixture of the fluorinated and non-fluorinated treating agents is simultaneously applied to the silica, or may be concentrated at a specific portion of the silica surface when treated separately or sequentially as needed using a suitable treatment process or by treating the silica in situ. Alternatively, the fluorinated hydrophobizing agent may be at least 30 wt.% of the total weight of reinforcing silica (B), alternatively at least 40 wt.% of the total weight of reinforcing silica (B), alternatively at least 50 wt.% of the total weight of reinforcing silica (B), alternatively at least 60 wt.% of the total weight of reinforcing silica (B), alternatively at least 80 wt.% of the total weight of reinforcing silica (B), or alternatively 100 wt.% of the total weight of reinforcing silica (B). In the above, the maximum value in each example is the weight percent of the total weight of reinforcing silica (B).

[0058] the composition is cured using at least one cure package of component (C), (D), or a mixture of components (C) and (D); (C) is at least one organohydrogenpolysiloxane (C)(i), at least one hydrosilylation catalyst (C)(ii), and optionally at least one cure inhibitor (C)(iii); and (D) is at least one peroxide catalyst.

[0059] (C)(i) Organohydrogenpolysiloxane When present, component (C)(i) is an organohydrogenpolysiloxane that functions as a crosslinker to cure component (A) by addition reaction of silicon-bonded hydrogen atoms in component (C)(i) with alkenyl groups in component (A) under the catalytic activity of component (C)(ii). Typically, component (C)(i) contains three or more silicon-bonded hydrogen atoms so that its hydrogen atoms can react sufficiently with the alkenyl groups in component (A) to form a network structure, thereby curing the composition. Alternatively, when component (A) has more than two alkenyl or alkynyl, or alkenyl groups per molecule, some or all of component (C)(i) may have two silicon-bonded hydrogen atoms per molecule.

[0060] The molecular structure of component (C)(i) is not particularly limited and may be linear, branched linear, or cyclic. The viscosity of this component is not particularly limited, but typically, to obtain good miscibility with component (A), it may be 0.001 to 50 Pa.s at 25°C using the most appropriate spindle for the viscosity range in the Brookfield® RV or LV range according to the cup / spindle method of ASTM D1084 Method B.

[0061] Component (C)(i) is typically added in an amount such that the molar ratio of the total number of silicon-bonded hydrogen atoms in component (C)(i) to all alkenyl and alkynyl groups, or the total number of alkenyls, in component (A) is 0.5:1 to 20:1. If this ratio is less than 0.5:1, an adequately cured composition cannot be obtained. If this ratio exceeds 20:1, the hardness of the cured composition tends to increase when heated. The silicon-bonded hydrogen (Si-H) content of organohydrogenpolysiloxane (C)(i) is determined using quantitative infrared analysis according to ASTM E168.

[0062] Examples of component (C)(i) 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 / 2 a copolymer consisting of units, (vi)(CH3)3SiO 1 / 2 Units: (CH3)2HSiO 1 / 2 units, and SiO 4 / 2 copolymers consisting of units, and (vii) (CH3)2HSiO above 1 / 2 Units and (R 2 Z) d (R 3 ) e SiO (4-d-e) / 2 Examples of copolymers include, but are not limited to, copolymers containing:

[0063] Typically, component (C)(i) is present in the composition in an amount of 0.5 to 10 weight percent of the total composition, which amount is determined depending on the desired molar ratio of the total number of silicon-bonded hydrogen atoms in component (C)(i) to the total number of all alkenyl and alkynyl groups, as discussed above.

[0064] (C)(ii) Hydrosilylation Catalyst When present, the hydrosilylation catalyst (C)(ii) 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.

[0065] Examples of preferred hydrosilylation catalysts (C)(ii) include, but are not limited to, platinum black, platinum on various solid supports, chloroplatinic acid, alcohol solutions of chloroplatinic acid, and complexes of chloroplatinic acid with ethylenically unsaturated compounds such as olefins and organosiloxanes containing ethylenically unsaturated silicon-bonded hydrocarbon groups. Catalyst (C)(ii) may be 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.

[0066] 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) a platinum-containing catalyst 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 platinum divinyltetramethyldisiloxane complexes typically containing about 1% by weight of platinum in a solvent such as toluene, are described in US Pat. No. 3,715,334 and US Pat. No. 3,814,730.

[0067] When present, the hydrosilylation catalyst (C)(ii) 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 the hydrosilylation catalyst (C)(ii) can be used to adjust the reaction rate and cure reaction rate. The catalytic amount of the hydrosilylation catalyst (C)(ii) is generally from 0.01 parts per million (ppm) to 10,000 parts by weight; alternatively, from 0.01 to 5000 ppm; alternatively, from 0.01 to 3,000 ppm; alternatively, from 0.01 to 1,000 ppm of platinum group metal, based on the combined weight of components (a) and (b) of the composition. In certain embodiments, the catalytic amount of the catalyst ranges from 0.01 to 1,000 ppm, alternatively, from 0.01 to 750 ppm, alternatively, from 0.01 to 500 ppm, alternatively, from 0.01 to 100 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.

[0068] Inhibitor (C)(iii) The compositions of components (A), (C)(i), and (C)(ii) can initiate cure at ambient temperatures. To extend the working or pot life of the hydrosilylation-curable composition, a suitable hydrosilylation reaction inhibitor (C)(iii) may be used to retard or inhibit the activity of the catalyst when (C)(i) and (C)(ii) are present. Hydrosilylation reaction inhibitors are well known in the art and 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 ene-ynes, hydroperoxides, nitriles, and diaziridines.

[0069] One class of known hydrosilylation reaction inhibitors includes the acetylenic compounds disclosed in U.S. Patent No. 3,445,420. Acetylenic alcohols, such as 2-methyl-3-butyn-2-ol, are 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.

[0070] Examples of acetylene 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, 1-phenyl-2-propyn-1-ol, 3,5-dimethyl-1-hexyn-3-ol, 1-ethynylcyclopentanol, 3-methyl-1-penten-4-yn-3-ol, and mixtures thereof. Derivatives of acetylene alcohols may include those compounds having at least one silicon atom.

[0071] When present, in some cases, inhibitor concentrations as low as 1 mole of inhibitor per mole of metal in catalyst (C)(ii) provide sufficient storage stability and cure speed. In other cases, inhibitor concentrations of up to 500 moles of inhibitor per mole of metal in catalyst (C)(ii) are necessary. The optimum concentration for a given inhibitor in a given composition is readily determined by routine experimentation. When present in the composition, inhibitors are typically present in amounts of 0.0125 to 10 weight percent of the composition, depending on the concentration and form in which the selected inhibitor is provided / commercially available.

[0072] When the composition relies on component C to cure, it is typically stored in two parts, often referred to as Parts A and B, for the purpose of separating components (C)(i) and (C)(ii) prior to curing. Typically, component (C)(iii), if present, is present in the same part as the crosslinker (C)(i). Such two-part compositions are designed for easy mixing immediately prior to use, and typically have a weight ratio of Part A:Part B of 15:1 to 1:1.

[0073] (D) Peroxide catalyst The compositions described herein may alternatively or additionally be cured with a peroxide catalyst (D) or a mixture of different types of peroxide catalysts.

[0074] The peroxide catalyst may be any of the well-known commercially available peroxides used to cure fluorosilicone elastomer compositions. The amount of organic peroxide used will depend on the nature of the cure process, the organic peroxide used, and the composition used. Typically, the amount of peroxide catalyst used in the compositions described herein is 0.2 to 3 wt.%, alternatively 0.2 to 2 wt.%, in each case based on the weight of the composition.

[0075] Suitable organic peroxides are substituted or unsubstituted dialkyl, alkylaroyl, and diaroyl peroxides, such as benzoyl peroxide and 2,4-dichlorobenzoyl peroxide, ditertiarybutyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, bis(t-butylperoxyisopropyl)benzene, bis(t-butylperoxy)-2,5-dimethylhexyne, 2,4-dimethyl-2,5-di(t-butylperoxy)hexane, di-t-butyl peroxide, and 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane. Mixtures of the above may also be used.

[0076] Optional Additional Ingredients Additional optional ingredients may be present in the silicone rubber composition depending on its intended use. Examples of such optional ingredients include thermally conductive fillers, non-conductive fillers, pot life extenders, flame retardants, lubricants, non-reinforcing fillers, compression set additives, pigments, colorants, adhesion promoters, chain extenders, silicone polyethers, mold release agents, diluents, solvents, UV light stabilizers, disinfectants, wetting agents, heat stabilizers, compression set additives, plasticizers, and mixtures thereof.

[0077] A pot life extender such as a triazole may be used, but is not considered essential within the scope of the present invention, and therefore the liquid curable silicone rubber composition may be free of a pot life extender.

[0078] Examples of flame retardants include aluminum trihydrate, magnesium hydroxide, chlorinated paraffins, hexabromocyclododecane, triphenyl phosphate, dimethylmethylphosphonate, tris(2,3-dibromopropyl)phosphate (brominated tris), and mixtures or derivatives thereof.

[0079] Examples of lubricants include graphite, talc, boron nitride, molybdenum disulfide, and mixtures or derivatives thereof.

[0080] Further additives include silicone fluids such as trimethyl- or dimethylhydroxy-terminated siloxanes, which typically have a viscosity of <150 mPa.s at 25°C by the cup / spindle method of ASTM D1084 Method B using the most appropriate spindle in the Brookfield® RV or LV range for that viscosity range. Such silicone fluids, when present, may be present in the liquid curable silicone rubber composition in an amount ranging from 0.1 to 5 weight percent (wt%), based on the total weight of the composition.

[0081] Examples of pigments include titanium dioxide, chromium oxide, bismuth vanadium oxide, iron oxide, and mixtures thereof.

[0082] 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 chelate compounds, such as zirconium(IV) tetraacetylacetonate, zirconium(IV) hexafluorophosphate, tetrakis(ethyltrifluoroacetylacetonate)zirconium, tetrakis(2,2,6,6-tetramethylheptanethionate)zirconium, zirconium(IV) dibutoxybis(ethylacetonate), diisopropoxybis(2,2,6,6-tetramethylheptanethionate)zirconium, or β-diketones (including alkyl- and fluorine-substituted forms thereof) and 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.

[0083] 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) together by reacting with the alkenyl groups of component (A), increasing the effective molecular weight and the distance between potential crosslinking sites.

[0084] 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 and fluorine content, 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), 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).

[0085] Further examples of chain extenders include tetramethyldihydrogendisiloxane or dimethylhydrogen-terminated polydimethylsiloxane.

[0086] The chain extender may be added in an amount of 1 to 10 parts by weight based on the weight of component (A), typically 1 to 10 parts per 100 parts of component (A).

[0087] Examples of heat stabilizers include metal compounds such as red iron oxide, yellow iron oxide, ferric hydroxide, cerium oxide, cerium hydroxide, lanthanum oxide, copper phthalocyanine, aluminum hydroxide, fumed titanium dioxide, iron naphthenate, cerium naphthenate, cerium dimethylpolysilanolate, and acetylacetonate salts of metals selected from copper, zinc, aluminum, iron, cerium, zirconium, titanium, etc. The amount of heat stabilizer present in the composition can range from 0.01 to 1.0 weight percent of the total composition.

[0088] Accordingly, the present invention provides a silicone rubber composition comprising: Component (A) in an amount of 40 to 95% by weight of the composition. A silicone rubber composition is provided comprising component (B) in an amount of 5 to 60 weight percent of the composition, the total weight percent of the composition being 100 weight percent for any composition.

[0089] When the composition cures via hydrosilylation, the composition may contain 0.5-10 wt. % of component (C)(i), 0.01-1 wt. % of component (C)(ii), and 0-1 wt. % of component (C)(iii). The total weight percent of the composition is 100 wt. % for any composition. In such cases, the composition is stored in two parts, Part A and Part B, prior to use. Typically, Part A contains a portion of component (A), a portion of component (B), and component (C)(ii), while Part B contains the remainder of components (A) and (B) along with component (C)(i). If present, optional inhibitor (C)(iii) may be present in either or both the Part (A) or Part (B) compositions. Optional components present in the composition may be incorporated into either or both the Part A or Part B compositions, as desired, as long as they do not have any adverse effect on the corresponding part. The two-part composition can be designed to be mixed together in any suitable ratio, for example, 15:1 to 1:1. When the ratio is 15:1 or greater, Part B can include only the crosslinker (C)(i) and optionally the inhibitor (C)(iii).

[0090] The curable silicone elastomer composition is (i) preparing a silicone-based composition by mixing a non-fluorinated polydiorganosiloxane (A) with at least one reinforcing silica filler; (ii) introducing component (C), component (D), or a mixture of component (C) and component (D), and storing the resulting composition, wherein if the composition contains a hydrosilylation cure package (C), the composition is stored in two or more parts in which components (C)(i) and (C)(ii) are maintained in separate parts; The at least one reinforcing silica filler is at least partially treated with a fluorination treating agent as described above before or during step (i).

[0091] In one embodiment, the reinforcing silica filler is treated with a treating agent prior to step (i) of the process. In this embodiment, all of the reinforcing silica filler is treated with a fluorinated treating agent prior to step (i), or alternatively, the reinforcing silica filler is partially treated with a fluorinated treating agent prior to step (i), and the remainder is treated with a non-fluorinated treating agent prior to step (i). In this embodiment, the reinforcing silica filler is treated prior to step (i), and then the treated reinforcing silica filler is mixed with non-fluorinated polydiorganosiloxane (A) to form the base resulting from step (i) of the process. In a further alternative, the silica may be treated with a mixture of fluorinated and non-fluorinated treating agents simultaneously or sequentially.

[0092] In an alternative embodiment, the non-fluorinated polydiorganosiloxane (A) may be divided into a plurality of predetermined aliquots, and each aliquot may be mixed in situ with a predetermined amount of reinforcing silica filler and fluorinated or non-fluorinated treating agent, such that multiple part bases are prepared in which the reinforcing silica filler is treated in situ, and the multiple part bases are subsequently mixed together to obtain the final product of step (i). In this embodiment, at least one aliquot of the non-fluorinated polydiorganosiloxane (A) is mixed with the fluorinated treating agent.

[0093] In an alternative embodiment, the non-fluorinated polydiorganosiloxane (A) is mixed in situ with one or more aliquots of reinforcing silica filler and one or more aliquots of fluorinated treating agent, such that the reinforcing silica filler is treated in situ to provide the final product of step (i).

[0094] In an alternative embodiment, the reinforcing silica filler is treated in situ to obtain the final product of step (i), wherein the non-fluorinated polydiorganosiloxane (A) is mixed in situ with one or more aliquots of the reinforcing silica filler and one or more aliquots of a mixture of 0-100 wt. % fluorinated treating agent and 0-100 wt. % non-fluorinated treating agent, such that, on average, at least 20 wt. % of the silica is treated with the fluorinated treating agent.

[0095] The resulting product of step (i) can be divided for use as a Part A base and a Part B base. Alternatively, two separate bases can be prepared at the end of step (i) as the composition is hydrosilylation cured. These can have the same or different compositions. For example, the Part A base composition can utilize a fluorinated treating agent, a non-fluorinated treating agent, or a mixture of such fluorinated and non-fluorinated treating agents. Similarly, the Part B base composition can utilize a fluorinated treating agent, a non-fluorinated treating agent, or a mixture of fluorinated and non-fluorinated treating agents. In either case, at least the Part A base composition or the Part B base composition will contain a reinforcing silica filler that has been at least partially treated with a fluorinated treating agent.

[0096] Regardless of the method for achieving the above, the amount of fluorinated treating agent treated reinforcing silica filler present in the composition is designed to provide, upon cure, an elastomeric product having a volume resistivity within a predetermined range to match that of adjacent cable insulation, e.g., cross-linked polyethylene.

[0097] For this purpose, any mixing technique and device described in the prior art can be used. The specific equipment used will depend on the viscosity of the individual components and the final curable coating composition. Suitable mixers include, but are not limited to, paddle-type mixers or kneader-type mixers. It may be desirable to cool the components during mixing to avoid premature curing of the composition.

[0098] When the compositions herein are designed to be LSR compositions, the viscosity of the compositions is 10 -1 seconds using a cone-and-plate rheometer, or if (A) contains at least one gum, by Williams plasticity measurement of the most viscous material, in each case in the range of 10 to 1,000 Pa.s, alternatively 10 to 500 Pa.s, alternatively 100 to 500 Pa.s, in each case at 25°C.

[0099] Alternatively, the 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 coating, or blow molding.

[0100] Curing of the curable silicone rubber composition may be carried out as needed depending on the type of silicone rubber used. Typical curing temperatures can range from 80 to 200°C, or alternatively, from 100 to 170°C. Curing times vary depending on the curing temperature and method selected, but are typically about 5 minutes to 1 hour. Furthermore, if necessary, the resulting cured elastomer can be post-cured. If desired, any suitable post-curing procedure can be performed. For example, the cured elastomer may be post-cured in an oven at a temperature of 150 to 250°C, or alternatively, from 170 to 230°C, for a predetermined period of time, for example, 2 to 10 hours, as needed.

[0101] Curing may occur, for example, in a mold to form a molded silicone article. The composition may be, for example, injection molded to form the article, or the composition may be overmolded by injection molding around an article or onto a substrate.

[0102] Also provided herein is a high voltage or high voltage DC insulator comprising an elastomeric product of the curable silicone elastomer composition described herein, and / or an elastomeric product obtained by curing the silicone elastomer composition described herein. Typically, the composition contains no more than (≦) 0.1% by weight of the composition of conductive or semiconductive filler or mixtures thereof, and in one embodiment, the composition contains 0 (zero)% by weight of conductive filler.

[0103] The cured composition can be used, for example, as a high-voltage insulator adapted to reduce electrical stress in high-voltage direct current (HVDC) applications, i.e., power cable systems, etc. As previously mentioned, a high-voltage insulator, or high-voltage DC insulator, is provided comprising an elastomeric product of the silicone elastomer composition described herein. The high-voltage insulator, or high-voltage DC insulator, may be used alone or may form a part of an article or assembly, e.g., a composite part of an assembly, such as in cable accessories, such as cable joints or cable termination materials, boots, sleeves, and / or other fittings, in field grading assemblies as a suitable insulating layer, and in other suitable cable accessories and connectors in HVDC applications.

[0104] In a further embodiment, there is provided a method of manufacturing an insulator or a field grading assembly including the insulator for a high voltage insulator application, or for a high voltage direct current (HVDC) insulator application, comprising the steps of: i) molding a suitable amount of a silicone composition as described above by suitable means, for example by extrusion or using a mold; and ii) curing the molded composition to form the molded insulator or field grading assembly including the insulator.

[0105] The high voltage or high voltage DC insulators described above may be part of a cable accessory for high voltage DC applications, such as a cable joint, cable terminal or cable connector, which may seal the end of a cable having a thermoplastic or rubber cable insulation.

[0106] The present invention further provides a method for sealing and / or insulating a connected cable or closed cable end by using a cable fitting as described above, comprising the steps of: (i) providing an insulated wire having a DC insulation and a suitable thermoplastic or elastomeric multi-layer sheath for the bare wire or connector; and (ii) encapsulating the bare wire or connector by placing it (i) on the surface of the insulating sheath in the bore of the tubular cable fitting pre-formed and cured as described above under the mechanical stretch of the fitting such that the overlap on the wire insulation between the molded silicone cable fitting and the sheath is greater than about 0.5 cm, whereby the silicone cable fitting seals the sheath insulation of the insulated wire under the mechanical pressure of the relaxed fitting and forms an encapsulating insulation on the bare wire and connector as well.

[0107] The compositions described herein can be used to manufacture a cable joint intended to seal the cable ends of one or more cables having thermoplastic polyolefin or rubber cable insulation, the cable joint sealing the cable ends of one or more cables having thermoplastic polyolefin or rubber cable insulation.

[0108] The compositions described above can be used in the manufacture of cable accessories, such as cable joints or cable termination materials in high-voltage direct current (HVDC) applications, such as HVDC power cable applications. The cured silicone composition according to the present invention can be used in the construction of any type of field grading assembly, such as geometric, capacitive, refractive, resistive, or nonlinear field grading assemblies for HVDC applications. The cured silicone composition can also be used in field grading assemblies for HVDC applications, where, in addition to the field grading material, it functions essentially or exclusively as an insulating layer, further contributing to the reduction of electrical stress. In certain cases, it can act as a field grading material, particularly in resistive field grading assemblies, cable joints, cable termination applications, cable accessories, and connectors.

[0109] For example, in the case of a high-voltage DC cable joint, a cable joint for connecting a pair of high-voltage DC power cables may be provided, including a means for receiving and connecting a pair of high-voltage DC cables, a layer of cable insulation adapted to surround the high-voltage DC cables when in the cable joint, and a layer of silicone rubber joint insulation material surrounding the cable insulation in the cable joint, the silicone rubber joint insulation being as described above and adapted to have a volume resistivity within a predetermined range of the volume resistivity of the cable insulation. Preferably, the cable insulation is made from cross-linked polyethylene. During assembly of the cable joint, the volume resistivity of the cable insulation is determined, for example, according to ASTM D257-14, which is the standard test method for DC resistance or conductance of insulating materials, and then a suitable silicone rubber joint insulation material designed to have a similar volume resistivity according to ASTM D257-14 is prepared as described herein. [Example]

[0110] In the following examples and compositions, unless otherwise noted, all viscosities are given at 25°C and were measured by the cup / spindle method of ASTM D1084 Method B using the Brookfield® RV or LV range spindle most appropriate for the viscosity range. Williams plasticity values ​​are provided in accordance with ASTM D-926-08. The vinyl and Si-H content of the polymers were measured by quantitative IR in accordance with ASTM E168.

[0111] Example 1 Liquid silicone rubber compositions using non-fluorinated polydiorganosiloxane polymers were prepared as LSR Base 1 and LSR Base 2, as shown in Table 1a below. The fumed silica was treated in situ during the preparation of the corresponding LSR base.

[0112] [Table 1]

[0113] LSR Base 1 and LSR Base 2 were mixed together in the ratios shown for Examples 1.1-1.8 in Table 1.b.

[0114] [Table 2]

[0115] The two base mixtures shown in Table 1b were then mixed with other ingredients to obtain a series of curable compositions incorporating various amounts of fluorinated filler-treated silica, as shown in Table 1c.

[0116] [Table 3]

[0117] Given that the samples were tested immediately, no two-part compositions were required, and the ingredients typically present in the Part B composition of a two-part composition as described above were mixed directly into the respective LSR Base 1 and LSR Base 2 alternative mixtures according to Table 1c above.

[0118] Different samples were prepared that were produced when the curable sheet was press-cured at 120°C for 10 minutes to form a cured sheet with a thickness of 0.5 mm. The volume resistivity was measured at room temperature with a polarization voltage of 1000V and a polarization time of 60 seconds. Note that 1.1 is the only example in Table 1b that does not contain silica treated with a fluorinated treating agent, and is therefore considered a comparative example.

[0119] Once cured, volume resistivity was measured on cured sheets ranging in thickness from 0.5 to 2 mm in accordance with ASTM D257-14: Standard Test Methods for DC Resistance or Conductance of Insulating Materials using a Keithley® 8009 test cell coupled to a Keithley® 5 1 / 2 digit Model 6517B electrometer / high resistance meter and controlled by Model 6524 high resistance measurement software: D257.

[0120] Within the Model 6524 High Resistance Measurement Software, alternating polarity testing was implemented as a "Hi-R" test to minimize the effects of background currents, as described in detail in the Keithley White Paper "Improving the Repeatability of Ultra-High Resistance and Resistivity Measurements" by Adam Daire.

[0121] To minimize the effects of background current, a Hi-R AC polarity test was used, a method designed to improve high resistance / resistivity measurements that are prone to large errors due to background current.

[0122] An alternating polarity stimulation voltage was used to separate the stimulation current from background current. When using the alternating polarity method, the voltage source output of the electrometer alternates between two voltages: offset voltage + AC V and offset voltage - AC V at specified intervals (measurement time).

[0123] A current measurement (Imeas) is taken at the end of each switch. After four Imeas values ​​are collected, a current reading is calculated (Icalc). Icalc is the binomial weighted average of the last four current measurements (Imeas1 through Imeas4). Icalc=(1 * Imeas1-3 * Imeas2+3 * Imeas3-1 * Imeas4) / 8 The symbols used for the four terms refer to the polarity of the AC portion of the voltage that generates the respective current. This calculation of the stimulation current is not affected by background current levels, gradients, or curvatures, effectively isolating the stimulation current from the background current. The result is a reproducible value of the stimulation current and resistance or resistivity calculated therefrom. The time dependence of the stimulation current is a material property; that is, different results will be obtained when using different measurement times due to material properties.

[0124] A measurement time of 60 seconds was used, typically with three voltage cycles of +1000 V then -1000 V. From the six measured currents obtained, the software obtains three Icalc values, the first of these is rejected and the next two values ​​are then used to calculate the volume resistivity (VR): VR=(V max -V min ) × area / (2 × I × sample thickness) Calculate from. The two resulting volume resistivity values ​​were averaged to obtain the final value, and the results for each combination are shown in Table 1d below.

[0125] [Table 4]

[0126] Here, Examples 1.2 to 1.8, which have different levels of silica filler treated with a fluorination treatment agent, exhibit lower volume resistivities than Comparative Example 1.1, which does not have silica filler treated with a fluorination treatment agent.

[0127] Additional samples of 1.2, 1.3, 1.4, 1.6, and 1.8 were prepared, where they were post-cured at 200°C for four hours (4h), and additional volume resistivity tests were performed at higher polarization voltages, longer polarization times, and higher temperatures, the results of which are provided in Table 1e below.

[0128] [Table 5]

[0129] Here, Examples 1.4, 1.6, and 1.8 continue to exhibit lower volume resistivities than Comparative Example 1.1 under various polarization voltages, polarization times, and temperatures.

[0130] Example 2: Example of high viscosity rubber High viscosity rubber bases were prepared. Blends of HCR1 and HCR2 having the compositions shown in Table 2a were prepared in various ratios as shown in Table 2b to provide Examples 2.1-2.8. The base compositions utilized are set forth in Table 2a below.

[0131] [Table 6]

[0132] HCR1 and HCR2 use a commercially available hydrosilylation cure catalyst package (XIAMETER™ Addition Cure package from Dow Silicones Corporation, Midland, Michigan, USA) rather than a standard peroxide curing agent, which includes a platinum catalyst, a Si-H-containing crosslinker, and a cure inhibitor. These components may be added in any suitable order; for example, the XIAMETER™ RBM-9200 inhibitor may be added first, followed by the XIAMETER™ RBM-9202 catalyst, and finally the XIAMETER™ RBM-9201 crosslinker. These are added sequentially, with the inhibitor (if present) added first. The catalyst must be well dispersed before being added. The crosslinker was added last.

[0133] For HCR3, which was cured using a peroxide catalyst, 100 parts by weight of the composition shown in Table 2a above was mixed with 1 part by weight of a 45% paste of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane in silicone, which is commercially available under various trade names such as DHBP-45-PSI (United Initiators). The resulting volume resistivity of HCR3 was measured as above and was found to be 8.12 x 10 13 It was found to be ohm-cm.

[0134] Hardened sheet Cured sheets were prepared at a thickness of 0.5 mm using a compression mold at a hydraulic pressure set at 300 psi (2.17 MPa) and a temperature of 120°C for 10 minutes, and the cured sheets were hung in a ventilated oven and post-cured at 200°C for up to 4 hours. Volume resistivity results for HCR1 and HCR2 sheets were determined as described above and are shown in Table 2b below.

[0135] [Table 7]

[0136] Here, Examples 2.3-2.8, which have various levels of silica filler treated with a fluorinated treating agent, exhibit lower volume resistivities than Comparative Examples 2.1 or 2.2, which do not have silica treated with a fluorinated siloxane.

[0137] Additional samples of 2.1, 2.6, and 2.7 were prepared, where they were post-cured at 200°C for up to 4 hours, and additional volume resistivity tests were performed at higher polarization voltages, longer polarization times, and higher temperatures, the results of which are provided in Table 2c below.

[0138] [Table 8]

[0139] Examples 2.6 and 2.7 continue to exhibit lower volume resistivities than Comparative Example 2.1 under various polarization voltages and polarization times.

[0140] Example 3 Liquid silicone rubber compositions using non-fluorinated polydiorganosiloxane polymers were prepared as LSR Base 3 and LSR Base 4, as shown in Table 3a below. Fumed silica was treated in situ during the preparation of the LSR Base or HCR.

[0141] [Table 9]

[0142] Materials were cured using the same formulations as shown in Table 1b, except that the mixture of LSR Base 1 and LSR Base 2 was replaced with either LSR Base 3 or LSR Base 4. Sheets of 0.5 mm thickness were cured at 120°C for 10 minutes and then measured for volume resistivity as described above, with the results shown in Table 3c below.

[0143] [Table 10]

[0144] Thus, these examples, in which the fumed silica is treated with a mixture of fluorinated and non-fluorinated treating agents, exhibit lower volume resistivities than those obtained for Example 1.4, in which LSR Bases 1 and 2 are blended after silica treatment. All examples exhibit a reduction in volume resistivity compared to Comparative Example 1.1, regardless of the method for preparing the mixture of fluorinated and non-fluorinated treating agents.

Claims

1. A curable silicone elastomer composition comprising: (A) at least one non-fluorinated polydiorganosiloxane in an amount of 40 to 95 weight percent of the composition; (B) at least one reinforcing silica filler at least partially hydrophobized with a fluorinated hydrophobizing agent in an amount of 5 to 60% by weight of the composition, wherein the fluorinated hydrophobizing agent is one or more silanol-terminated fluorinated siloxane oligomers having 2 to 20 siloxane units, and / or one or more fluorinated silanediols, and / or one or more fluorinated trialkoxysilanes, or mixtures thereof; At least one reinforcing silica filler selected from (D) The composition wherein (D) is at least one peroxide catalyst in an amount of 0.2 to 3 weight percent, based on the weight of the composition.

2. containing ≦0.1% by weight of the composition of a conductive or semiconductive filler or mixture thereof, the presence of at least two alkenyl or alkynyl groups per molecule in (A) being optional when component (D) is the only catalyst; and / or 2. The curable silicone elastomer composition of claim 1, wherein filler (B) has been at least partially treated with one or more fluorination treating agents selected from the group consisting of trifluoropropyltrimethoxysilane and trifluoropropyltriethoxysilane; and silanol-terminated trifluoropropylalkylsiloxanes having 2 to 20 siloxane repeat units, wherein the alkyl group has 1 to 6 carbons, to render the filler hydrophobic.

3. A high voltage insulator comprising the elastomeric product of the curable silicone elastomer composition of claim 1.

4. A high voltage insulator comprising an elastomeric product obtained or obtainable by curing the silicone elastomer composition of claim 1.

5. 5. The high voltage insulator of claim 3 or 4 for use as an insulator adapted to reduce electrical stress in high voltage direct current (HVDC) applications.

6. 5. The high voltage insulator of claim 3 or 4 used alone or as part of an article or assembly.

7. 7. The high voltage insulator of claim 6, wherein the article or assembly is a cable accessory, a cable joint or cable termination, a boot, a sleeve, and / or other fitting in a high voltage DC application.

8. 5. The high voltage insulator of claim 3 or 4, which is a high voltage DC insulator.

9. 10. A method for preparing the curable silicone elastomer composition of claim 1, comprising: (i) preparing a silicone-based composition by mixing a non-fluorinated polydiorganosiloxane (A) with at least one reinforcing silica filler; by introducing component (D) and storing the resulting composition; The method of claim 1, wherein said at least one reinforcing silica filler is at least partially treated with a fluorination treating agent prior to or during step (i).

10. 10. A method for preparing a curable silicone elastomer according to claim 9, comprising treating the reinforcing silica filler with a treating agent prior to step (i), treating all of the reinforcing silica filler with a fluorinated treating agent prior to step (i), or treating a portion of the reinforcing silica filler with a fluorinated treating agent prior to step (i) and treating the remainder with a non-fluorinated treating agent prior to step (i); or dividing the non-fluorinated polydiorganosiloxane (A) into a plurality of predetermined aliquots, each of which may be mixed in situ with a predetermined amount of reinforcing silica filler and a fluorinated or non-fluorinated treating agent, so as to prepare a plurality of part bases in which the reinforcing silica filler is treated in situ, and subsequently mixing the plurality of part bases together to obtain the final product of step (i); or mixing the non-fluorinated polydiorganosiloxane (A) in situ with the reinforcing silica filler and the fluorination treating agent so as to treat the reinforcing silica filler in situ to obtain the final product of step (i); or mixing said non-fluorinated polydiorganosiloxane (A) in situ with said reinforcing silica filler and a mixture of fluorinated and non-fluorinated treating agents so as to treat said reinforcing silica filler in situ to obtain the final product of step (i).

11. 11. A method for producing high voltage DC insulators according to claim 9 or 10, wherein the composition is introduced into a mold before curing to form a molded silicone article.

12. 11. A method for producing high voltage DC insulators according to claim 9 or 10, wherein the composition is injection molded to form an article or overmolded by injection molding around an article.

13. 10. Use of the curable silicone elastomer composition of claim 1 in or as a high voltage DC insulator.

14. 14. Use of the silicone composition of claim 13 to reduce electrical stress in high voltage direct current (HVDC) applications.

15. 15. Use of the silicone composition according to claim 13 or 14 as an insulator for high voltage direct current (HVDC) applications.

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