Liquid silicone rubber composition

Abstract

The present disclosure relates to a hydrosilylation (addition) curable silicone rubber composition which, upon curing, provides a silicone elastomer material having improved low compression set while avoiding the need for a post-curing step, and a method for preparing such a silicone elastomer material. The present disclosure also relates to the use of such materials in the manufacture of or for the manufacture of silicone coatings for standard non-silicone insulators, the use of such materials as cable coatings, for example for safety cables, and extends to the use of such materials in cable accessories such as electrical connectors, connector seals, terminals and wire seals, particularly for the automotive industry.

Description

Technical Field

[0001] The present disclosure relates to a hydrosilylation (addition) curable silicone rubber composition which, upon curing, provides a silicone elastomer material with improved low compression set while avoiding the need for a post-curing step, a hydrosilylation (addition) curable silicone rubber composition, and a method for preparing such a silicone elastomer material. The present disclosure also extends to the use of such materials in the manufacture of silicone coatings for standard non-silicone insulators or for their use in the manufacture, their use as cable coatings, for example, for safety cables, in cable accessories such as electrical connectors, connector seals, terminals and wire seals, particularly for the automotive industry, and / or in hoses and gaskets, for example, for vehicle engines.

Background Art

[0002] A hydrosilylation curable silicone rubber composition comprising (i) an organopolysiloxane polymer having unsaturated (alkenyl and / or alkynyl) groups, (ii) a compound containing silicon-bonded hydrogen atoms, and (iii) a hydrosilylation catalyst, It is used to prepare silicone elastomer materials that are known in the art and have a wide range of physical properties including electrical insulation, heat resistance and thermal stability, frost resistance, abrasion resistance, flame retardancy, and long-term flexibility. Due to this unique combination of properties, elastomers made from liquid silicone rubber are suitable for use in a wide range of electrical and / or insulation applications such as the above-mentioned uses, and in addition to applications such as electrical insulation and / or thermal stability, many of these applications require the silicone elastomer material to have low compression set. For example, automobiles are increasingly dependent on electrical and electronic systems for their proper operation, and even more so since the introduction of electric and hybrid vehicles. Therefore, electrical failures can lead to malfunctions of devices such as radios, lights, ventilation, etc., or even further failures. Many electrical connectors rely on the aforementioned silicone rubber materials to prevent electrical failures and need to be able to avoid failures when the engine temperature rises.

[0003] Compression set is an important property of silicone elastomer materials used in any of the above applications. Compression set is the thermally induced fatigue behavior of a silicone elastomer material, which can be defined as the loss of the ability of the silicone elastomer material to recover to its original thickness after being compressed at the curing (elevated) temperature for a specific period. The compression set value can be measured, for example, according to industrial standard ISO815-1:2019 Method A, B or C and is specified as a percentage. For example, if there is complete recovery, i.e., the thickness of the test piece is the same before and after the application of the load, the compression set is 0%. In contrast, if 25% compression of the silicone elastomer material applied during the test remains unchanged when the load is removed, the compression set is 100% because it does not return to its original shape at all. Without being bound by current theory, the fundamental reason why a silicone-based elastomer material cannot recover to its original thickness after being compressed at the curing (high) temperature for a specific period is thought to be that the hydrosilylation-curable silicone composition often does not undergo complete curing during the standard curing process, if not always. This is thought to be due, at least in part, to incomplete hydrosilylation due to steric hindrance during the interaction of the vinyl-containing silicone polymer, the Si-H crosslinking agent, and the hydrosilylation catalyst (most typically a platinum-based catalyst). Therefore, when a hydrosilylation-cured silicone elastomer material is compressed at high temperature, further crosslinking can occur within the body of the silicone elastomer material, specifically at Si-H sites that were previously unreacted. Furthermore, intermolecular bond formation can occur between polydimethylsiloxane (PDMS) chains, specifically also at Si-H excess sites that were previously unreacted here (via hydrolysis, oxidation or thermally induced reaction pathways), and thermo-oxidative rearrangement can occur within or between the individual PDMS chains of the silicone elastomer material.One or more of the above occurrences causes an increase in the crosslink density within the silicone elastomer material, resulting in a more rigid structure that prevents the silicone elastomer material from returning to its original thickness after compression.

[0004] Many silicone elastomer materials have a large compression set, for example, greater than 50%, and even greater than 60%, even after being compressed for a short period of 22 hours each at temperatures of 125 °C and 150 °C, and are subject to problems caused by a consequential change in shape and / or a significant increase in hardness during long-term use in high-temperature applications unless they undergo a post-cure heating process. "Post-curing" is the simplest way to minimize compression set, in which case hydrosilylation-cured silicone materials are subjected to post-cure heating at 150 °C or higher for a period of several hours, for example, 4 hours or more. However, post-curing is usually not commercially desirable or is not actually feasible considering the increased energy consumption and the delay in manufacturing time.

[0005] Many of the above applications typically desire a silicone elastomer material that has a compression set value as low as possible, for example, 40% or less, or preferably 20% or less, after being compressed over a wide temperature range, for example, -40 °C to +175 °C, or even higher.

[0006] In the United States, an electrical connector system needs to meet the requirements of the test form of "Performance Specification for Automotive Electrical Connector Systems" of SAE International USCAR-2. The suitability of use of the shield connector assembly is rated over a specific temperature range. The T1 temperature class is for the temperature range of -40°C to +85°C, T2 is for the temperature range of -40°C to +100°C, T3 is for the temperature range of -40°C to +125°C, and in the temperature range of -40°C to 125°C, it meets the relevant automotive specifications of the T3 temperature class. T4 is for the temperature range of -40°C to +150°C, and the current highest grade is T5 for the temperature range of -40°C to 175°C. Considering that it is not desirable to post-cure all elastomers after curing, various additives have been proposed to reduce compression set without the need for post-curing. In U.S. Patent No. 5,153,244, the compression set value of the hydrosilylation-cured silicone was substantially reduced by introducing a phthalocyanine compound or a metal derivative of such a compound (the metal was copper, nickel, cobalt, or iron) into the composition.

[0007] U.S. Patent No. 8,080,598 describes the use of metal deactivators selected from diacyl-hydrazide compounds such as dodecanedioyl-di-(N'-salicyloyl)hydrazine, which is synonymous with 1-N',12-N'-bis(2-hydroxybenzoyl)dodecanedihydrazide, aminotriazole compounds such as 3-(n-salicyloyl)amino-1,2,4-triazole, which is synonymous with 2-hydroxy-N-1H-1,2,4-triazol-3-ylbenzamide, or amino-containing triazine compounds, in combination with a curing inhibitor selected from acetylene-containing silanes, vinyl-containing low molecular weight organosiloxane compounds, or alcohol derivatives having a carbon-carbon triple bond, for the purpose of reducing compression set, to obtain a hydrosilylation-cured silicone rubber having a low compression set without post-curing. European Patent No. 0,517,524 and U.S. Patent No. 5,104,919 describe the use of different triazole derivatives and benzotriazole derivatives as additives for the controlled reduction of the compression set of hydrosilylation-cured silicone elastomers. U.S. Patent No. 5,977,249 describes the use of various organic sulfur compounds, particularly mercaptans, and U.S. Patent No. 9,200,146 describes the use of 3-amino-1,2,4-triazole-5-thiol bonded to silica for reducing compression set.

Summary of the Invention

[0008] This specification discloses a hydrosilylation-curable silicone rubber composition comprising the following components, namely: a) one or more polyorganosiloxanes containing at least two unsaturated groups selected from alkenyl groups and alkynyl groups per molecule and having a viscosity in the range of 1000 MPa·s to 100,000 MPa·s at 25°C; b) an organosilicon compound having at least two or at least three Si-H groups per molecule; c) an optionally hydrophobized silica reinforcing filler; d) a hydrosilylation catalyst containing or consisting of a platinum group metal or a compound thereof; e) R 1 -O-C(=O)-CH2CH2-S-CH2CH2-C(=O)-O-R 1 and C-(CH2OC(=O)-CH2CH2-S-R 1 )4 (wherein each R 1 may be the same or different and is an alkyl group), and at least one thiopropionate selected therefrom, and the total weight % of the composition is 100% by weight, a hydrosilylation-curable silicone rubber composition is provided.

[0009] A silicone elastomer material which is a cured product of the above hydrosilylation-curable silicone rubber composition, having a compression set of 20% or less after compression at a temperature up to 190 °C for 22 hours as measured according to the industrial standard specification ISO815-1:2019 Method A, is also provided.

[0010] A process for producing a silicone elastomer material, comprising the following components, namely, a) One or more polyorganosiloxanes containing at least two unsaturated groups selected from alkenyl groups and alkynyl groups per molecule and having a viscosity in the range of 1000 MPa·s to 100,000 MPa·s at 25 °C, b) An organosilicon compound having at least two or at least three Si-H groups per molecule; c) An optionally hydrophobized silica reinforcing filler, d) A hydrosilylation catalyst containing or consisting of a platinum group metal or a compound thereof, e) R 1 -O-C(=O)-CH2CH2-S-CH2CH2-C(=O)-O-R 1 and C(CH2OC(=O)-CH2CH2-S-R 1 )4 (wherein each R 1which may be the same or different and is an alkyl group), and mixing a hydrosilylation-curable silicone rubber composition having at least one thiopropionate selected therefrom, wherein the total weight % of the composition is 100% by weight, the step of mixing; and curing the composition at a temperature of 80°C to 200°C. A process is also provided.

[0011] Also provided is a silicone elastomer material comprising the following components, namely: a) at least two unsaturated groups selected from alkenyl groups and alkynyl groups per molecule, and having a viscosity in the range of 1000 MPa·s to 100,000 MPa·s at 25°C, one or more polyorganosiloxanes; b) an organosilicon compound having at least two or at least three Si-H groups per molecule; c) an optionally hydrophobic silica reinforcing filler; d) a hydrosilylation catalyst containing or consisting of a platinum group metal or a compound thereof; e) R 1 -O-C(=O)-CH2CH2-S-CH2CH2-C(=O)-O-R 1 and C-(CH2OC(=O)-CH2CH2-S-R 1 )4 (wherein each R 1 which may be the same or different and is an alkyl group), and mixing a hydrosilylation-curable silicone rubber composition having at least one thiopropionate selected therefrom, wherein the total weight % of the composition is 100% by weight, the step of mixing; and curing the composition at a temperature of 80°C to 200°C, and a silicone elastomer material obtained from or obtainable from the process, wherein the silicone elastomer material has a compression set of 20% or less after compression at a temperature up to 190°C for 22 hours as measured according to the industrial standard specification ISO815-1:2019 method A.

[0012] Use of at least one thiopropionate, wherein the at least one thiopropionate is R 1 -O-C(=O)-CH2CH2-S-CH2CH2-C(=O)-O-R 1 and C-(CH2OC(=O)-CH2CH2-S-R 1 )4 (wherein each R 1 may be the same or different), and the use is as a means for reducing the compression set in a silicone elastomer material which is a cured product of a hydrosilylation-curable silicone rubber composition, and the hydrosilylation-curable silicone rubber composition has, in other respects, the following components, namely, a) one or more polyorganosiloxanes containing at least two unsaturated groups selected from alkenyl groups and alkynyl groups per molecule and having a viscosity in the range of 1000 MPa·s to 100,000 MPa·s at 25°C, b) an organosilicon compound having at least two or at least three Si-H groups per molecule; c) an optionally hydrophobically treated silica reinforcing filler, d) a hydrosilylation catalyst containing or consisting of a platinum group metal or a compound thereof, Use of at least one thiopropionate is also provided, wherein the total weight percentage of the composition is 100% by weight.

[0013] The compositions described herein containing component (e) above have been found to provide silicone elastomers with consistently improved (lower) compression over a wide temperature range from 100 °C to about 190 °C compared to two of the most preferred commercially available compression set additives, namely the aforementioned dodecanedioyl-di-(N'-salicyloyl) hydrazide, which is synonymous with 1-N',12-N'-bis(2-hydroxybenzoyl)dodecane dihydrazide, and 3-(n-salicyloyl)amino-1,2,4-triazole, which is synonymous with 2-hydroxy-N-1H-1,2,4-triazol-3-ylbenzamide. A further advantage of the compositions containing component (e) as a compression set additive over many of the initial sulfur-containing compression set additives is that component (e) does not have an offensive odor. In contrast, other previously proposed sulfur-containing compression set additives cause the resulting silicone elastomers to have a sulfur odor that is not industrially acceptable.

Mode for Carrying Out the Invention

[0014] The components of the composition will be described in more detail below.

[0015] Component (a) Component (a) of the composition is one or more polyorganosiloxanes containing at least two unsaturated groups selected from alkenyl groups and alkynyl groups per molecule and having a viscosity in the range of 1000 MPa·s to 100,000 MPa·s at 25 °C.

[0016] Component (a) is a polydiorganosiloxane such as a polydiorganosiloxane having at least two unsaturated groups per molecule, and this unsaturated group is selected from alkenyl groups or alkynyl groups. Alternatively, component (a) has at least three unsaturated groups per molecule.

[0017] The unsaturated groups of component (a) may be located at the terminal, pendant, or both positions.

[0018] The alkenyl group may have 2 to 30, or 2 to 24, or 2 to 20, or 2 to 12, or 2 to 10, or 2 to 6 carbon atoms. Exemplary alkenyl groups include, but are not limited to, vinyl, allyl, methallyl, propenyl, and hexenyl groups, and cyclohexenyl groups.

[0019] The alkynyl group may have 2 to 30, or 2 to 24, or 2 to 20, or 2 to 12, or 2 to 10, or 2 to 6 carbon atoms. Exemplary alkynyl groups include, but are not limited to, ethynyl, propynyl, and butynyl groups.

[0020] Component (a) has a plurality of units of formula (I): R’ a SiO (4-a) / 2 (I), wherein each R’ is independently selected from an aliphatic hydrocarbyl group or an aliphatic non-halogenated organo group (the organo group is any aliphatic organic substituent having one free valence on a carbon atom, regardless of the type of functional group). Saturated aliphatic hydrocarbyls are exemplified by, but not limited to, alkyl groups such as methyl, ethyl, propyl, pentyl, octyl, undecyl, and octadecyl, and cycloalkyl groups such as cyclohexyl. Unsaturated aliphatic hydrocarbyls are exemplified by, but not limited to, the above alkenyl and alkynyl groups. Aliphatic non-halogenated organo groups are exemplified by, but not limited to, suitable nitrogen-containing groups such as amide and imide groups, oxygen-containing groups such as polyoxyalkylene, carbonyl, alkoxy, and hydroxyl groups. Further organo groups can include phosphorus-containing groups and boron-containing groups. The subscript “a” is 0, 1, 2, or 3, and typically in this case, a is mainly 2, but some units with a being 1 or 3 may also be included.

[0021] The siloxy units can be described by the omission (abbreviated) nomenclature, namely, "M", "D", "T", and "Q". When R' is as described above or is an alkyl group, typically a methyl group, the M unit is a siloxy unit where a = 3 in the formula, namely, R'3SiO 1 / 2 corresponds to, the D unit is a siloxy unit where a = 2 in the formula, namely, R'2SiO 2 / 2 corresponds to, the T unit is a siloxy unit where a = 1 in the formula, namely, R'1SiO 3 / 2 corresponds to, and the Q unit is a siloxy unit where a = 0 in the formula, namely, SiO 4 / 2 corresponds to. The polydiorganosiloxane such as the polyorganosiloxane of component (a) is substantially linear, but may contain a certain proportion of branches due to the presence of T units (as described above) in the molecule. Therefore, the average value of the subscript a in structure (I) is about 2.

[0022] Examples of typical R' groups on one or more polyorganosiloxanes of component (a) containing at least two unsaturated groups selected from alkenyl and alkynyl groups per molecule mainly include alkyl groups, especially methyl and ethyl, or a methyl group. However, in addition to at least two necessary unsaturated groups selected from alkenyl and / or alkynyl groups, typically alkenyl groups, aryl groups and / or fluoroalkyl groups, such as trifluoropropyl group or perfluoroalkyl group can also be mentioned. These groups may be in the pendant position (on the D or T siloxy unit) or at the terminal (on the M siloxy unit).

[0023] Accordingly, the polymer chain of component (a) may be selected from polydimethylsiloxane, alkylmethylpolysiloxane, alkylarylpolysiloxane or copolymers thereof (reference to alkyl means any suitable alkyl group or an alkyl group having two or more carbons), provided that each component (a) polymer contains at least two alkenyl groups and / or alkynyl groups, typically at least two alkenyl groups. Such a polymer chain may have any suitable end groups, for example, trialkyl end, alkenyldialkyl end, alkynyldialkyl end, or may be terminated with any other suitable combination of end groups, provided that each polymer contains at least two unsaturated groups selected from alkenyl groups and alkynyl groups per molecule. In one embodiment, the end groups of such polymers contain no silanol end groups at all.

[0024] Accordingly, component (a) may be, for example, the following: Dialkylalkenyl-terminated polydimethylsiloxane, for example, dimethylvinyl-terminated polydimethylsiloxane, dialkylalkenyl-terminated dimethylmethylphenylsiloxane, for example, dimethylvinyl-terminated dimethylmethylphenylsiloxane, trialkyl-terminated dimethylmethylvinylpolysiloxane, dialkylvinyl-terminated dimethylmethylvinylpolysiloxane copolymer, dialkylvinyl-terminated methylphenylpolysiloxane, dialkylalkenyl-terminated methylvinylmethylphenylsiloxane, dialkylalkenyl-terminated methylvinyl diphenylsiloxane, dialkylalkenyl-terminated methylvinylmethylphenyl dimethylsiloxane, trimethyl-terminated methylvinylmethylphenylsiloxane, trimethyl-terminated methylvinyl diphenylsiloxane, or trimethyl-terminated methylvinylmethylphenyl dimethylsiloxane.

[0025] Component (a) has a viscosity of 1000 mPa·s to 100,000 mPa·s at 25°C, or 5000 MPa·s to 75000 MPa·s at 25°C, or 10,000 mPa·s to 60,000 mPa·s at 25°C, and is preferably present in an amount of 25 to 60% by weight of the composition, or an amount of 30 to 60% by weight of the composition, or an amount of 35 to 55% by weight of the composition. The viscosity can be measured at 25°C using a Brookfield (trademark) rotational viscometer with spindle LV-4 (designed for viscosities in the range of 1,000 to 2,000,000 mPa·s) at an appropriate rpm for viscosities exceeding 15,000 mPa·s, or using a cone-plate configuration with cone CP-52 at an appropriate rpm for viscosities up to 15,000 mPa·s at 25°C with a Brookfield (trademark) rotational viscometer.

[0026] Component (b) Component (b) functions as a crosslinking agent and is provided in the form of an organosilicon compound having at least two, or at least three Si-H groups per molecule. Component (b) usually contains three or more silicon-bonded hydrogen atoms, and as a result, the hydrogen atoms can react with the unsaturated alkenyl and / or alkynyl groups of component (a) to form a network structure therewith, thereby enabling the composition to be cured. Alternatively, when polymer (a) has more than two unsaturated groups per molecule, some or all of component (b) may have two silicon-bonded hydrogen atoms per molecule.

[0027] The molecular structure of the organosilicon compound (b) having at least two, or at least three Si-H groups per molecule is not particularly limited. It may be a linear, branched-chain (linear with some branches through the presence of T groups), cyclic, or silicone resin-based polyorganosiloxane.

[0028] The molecular weight of component (b) is not particularly limited, but the viscosity is typically 5 to 50,000 mPa·s at 25°C using the test method described for component (a).

[0029] The silicon-bonded organic groups used in component (b) can be exemplified by alkyl groups such as methyl, ethyl, propyl, n-butyl, t-butyl, pentyl, hexyl; aryl groups such as phenyl, tolyl, xylyl, or similar aryl groups; 3-chloropropyl, 3,3,3-trifluoropropyl, or similar halogenated alkyl groups, and can preferably be an alkyl group having 1 to 6 carbons, particularly a methyl, ethyl, or propyl group, or a phenyl group. Preferably, the silicon-bonded organic group used in component (b) is an alkyl group, or a methyl group, an ethyl group, or a propyl group.

[0030] Examples of the organosilicon compound (b) having at least two or at least three Si-H groups per molecule include, but are not limited to, the following: (a’) Trimethylsiloxy-terminated methylhydrogenpolysiloxane, (b’) Trimethylsiloxy-terminated polydimethylsiloxane-methylhydrogensiloxane, (c’) Copolymer of dimethylhydrogensiloxy-terminated dimethylsiloxane-methylhydrogensiloxane, (d’) Cyclic copolymer of dimethylsiloxane-methylhydrogensiloxane, (e’)(CH3)2HSiO 1 / 2 unit, (CH3)3SiO 1 / 2 unit, and SiO 4 / 2 unit copolymer and / or silicone resin, (f’)(CH3)2HSiO 1 / 2 unit, and SiO 4 / 2 unit copolymer and / or silicone resin, (g’) Methylhydrogensiloxane cyclic homopolymer having 3 to 10 silicon atoms per molecule. Alternatively, component (b) which is a crosslinking agent can be a filler, for example, silica treated with one of the above, and mixtures thereof.

[0031] In one embodiment, component (b) is selected from methylhydrogenpolysiloxane blocked at both molecular ends with trimethylsiloxy groups; a copolymer of methylhydrogensiloxane and dimethylsiloxane blocked at both molecular ends with trimethylsiloxy groups; dimethylsiloxane blocked at both molecular ends with dimethylhydrogensiloxy groups; and a copolymer of methylhydrogensiloxane and dimethylsiloxane blocked at both molecular ends with dimethylhydrogensiloxy groups.

[0032] The crosslinking agent (b) is generally present in the hydrosilylation-curable silicone rubber composition such that the molar ratio of the total number of silicon-bonded hydrogen atoms in component (b) to the total number of alkenyl groups and / or alkynyl groups in component (a) is 0.5:1 to 10:1. When this ratio is less than 0.5:1, a fully cured composition cannot be obtained. When this ratio exceeds 10:1, the hardness of the cured composition tends to increase when heated. Preferably, component (b) is present in an amount such that the molar ratio of the silicon-bonded hydrogen atoms of component (b) to the alkenyl group / alkynyl group, or alkenyl group, of component (a) is in the range of 0.7:1.0 to 5.0:1.0, or 0.9:1.0 to 2.5:1.0, or further 0.9:1.0 to 2.0:1.0.

[0033] The silicon-bonded hydrogen (Si-H) content of component (b) is determined using quantitative infrared analysis in accordance with ASTM E168. In the case of the present invention, the ratio of silicon-bonded hydrogen to alkenyl (vinyl) and / or alkynyl is important when depending on the hydrosilylation curing process. Generally, this is determined by calculating the total weight % of alkenyl groups, for example, vinyl [V] in the composition and the total weight % of silicon-bonded hydrogen [H] in the composition. When the molecular weight of hydrogen is 1 and the molecular weight of vinyl is 27, the molar ratio of silicon-bonded hydrogen to vinyl is 27[H] / [V].

[0034] Typically, depending on the number of unsaturated groups in component (a) and the number of Si-H groups in component (b), component (b) is present in an amount of 0.1 to 10% by weight of the hydrosilylation-curable silicone rubber composition, or 0.1 to 7.5% by weight of the hydrosilylation-curable silicone rubber composition, or 0.5 to 7.5% by weight of the hydrosilylation-curable silicone rubber composition, or further 0.5% to 5% by weight.

[0035] Component (c) Component (c) is a silica reinforcing filler which is optionally hydrophobically treated. The reinforcing filler of component (c) can be exemplified by fumed silica and / or precipitated silica and / or colloidal silica. In one alternative, the fumed silica, precipitated silica and / or colloidal silica are provided in a micronized form.

[0036] Precipitated silica, fumed silica and / or colloidal silica are particularly preferred because their surface area is relatively high, typically at least 50 m 2 / g (BET method according to ISO9277:2010). Typically, fillers having a surface area of 50 to 450 m 2 / g (BET method according to ISO9277:2010), or 50 to 300 m 2 / g (BET method according to ISO9277:2010) are used. All of these types of silica are commercially available.

[0037] When the silica reinforcing filler (c) is originally hydrophilic (for example, an untreated silica filler), it is typically treated with a treating agent to make it hydrophobic. These surface-modified silica reinforcing fillers (c) do not aggregate, and due to the surface treatment, the filler can be easily wetted by component (a), and thus can be homogeneously incorporated into the polydiorganosiloxane polymer (a) described below.

[0038] Typically, the silica reinforcing filler (c) may be surface-treated with any low molecular weight organosilicon compound disclosed in the art applicable to preventing the creping of the liquid silicone rubber (LSR) composition during processing. For example, organosilanes, polydiorganosiloxanes, or organosilazanes, such as hexaalkyldisilazanes, short-chain siloxane diols, which make the silica reinforcing filler (c) hydrophobic, and as a result, easier to handle and obtain a homogeneous mixture with other raw materials. Specific examples include silanol-terminated trifluoropropylmethylsiloxane, silanol-terminated vinyl methyl (ViMe) siloxane, silanol-terminated methyl phenyl (MePh) siloxane, liquid hydroxyl dimethyl-terminated polydiorganosiloxane containing an average of 2 to 20 repeating units of diorganosiloxane in each molecule, hydroxyl dimethyl-terminated phenylmethylsiloxane, hexaorganodisiloxanes such as hexamethyldisiloxane, divinyltetramethyldisiloxane; hexaorganodisilazanes such as hexamethyldisilazane (HMDZ), divinyltetramethyldisilazane, and tetramethyldi(trifluoropropyl)disilazane; hydroxyl dimethyl-terminated polydimethylmethylvinylsiloxane, octamethylcyclotetrasiloxane, and silanes including, but not limited to, methyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, chlorotrimethylsilane, dichlorodimethylsilane, trichloromethylsilane.

[0039] In one embodiment, the treating agent can be selected from silanes such as silanol-terminated vinylmethyl (ViMe) siloxane, liquid hydroxyl dimethyl-terminated polydiorganosiloxane containing on average 2 to 20 repeating units of diorganosiloxane in each molecule, hexaorganodisiloxanes such as hexamethyldisiloxane, divinyltetramethyldisiloxane; hexaorganodisilazanes such as hexamethyldisilazane (HMDZ), divinyltetramethyldisilazane; and hydroxyl dimethyl-terminated polydimethylmethylvinylsiloxane, octamethylcyclotetrasiloxane, and methyltriethoxysilane, dimethyldiethoxysilane, and / or vinyltriethoxysilane, but is not limited thereto. A small amount of water can be added together with the silica treating agent as a processing aid.

[0040] The surface treatment of the untreated silica reinforcing filler (c) can be carried out before introduction into the composition or in situ (i.e., by blending these raw materials together at room temperature or higher in the presence of at least some of the other raw materials of the composition of the present specification until the filler is completely treated). Typically, the untreated silica reinforcing filler (c) is treated in situ with the treating agent in the presence of component (a), thereby preparing a silicone rubber base material that can be subsequently mixed with other components.

[0041] The silica reinforcing filler (c) is optionally present in an amount of up to 40% by weight of the composition, or 1.0 to 40% by weight of the composition, or 5.0 to 35% by weight of the composition, or 10.0 to 35% by weight of the composition.

[0042] Component (d) Component (d) of the composition is a hydrosilylation catalyst containing or consisting of a platinum group metal or a compound thereof. They are usually selected from the metals of the platinum group (platinum, ruthenium, osmium, rhodium, iridium, and palladium), or catalysts of one or more compounds of such metals. Alternatively, platinum and rhodium compounds are preferred due to the high activity levels of these catalysts in the hydrosilylation reaction, and platinum compounds are most preferred. In the hydrosilylation (or addition) reaction, a hydrosilylation catalyst such as component (d) herein catalyzes the reaction between an unsaturated group, usually an alkenyl group such as vinyl, and an Si-H group.

[0043] Catalyst (d) can be a platinum group metal, a platinum group metal deposited on a carrier such as activated carbon, a metal oxide such as aluminum oxide or silicon dioxide, silica gel or powdered carbon, or a compound or complex of a platinum group metal. Preferably, the platinum group metal is platinum.

[0044] Examples of preferred hydrosilylation catalysts (d) are platinum-based catalysts such as platinum black, platinum oxide (Adams catalyst), platinum on various solid supports, chloroplatinic acid, for example hexachloroplatinic acid (Pt oxidation state IV) (Speier catalyst), chloroplatinic acid in a solution of an alcohol such as isooctanol or amyl alcohol (Lamoreaux catalyst), and complexes of chloroplatinic acid with ethylenically unsaturated compounds such as olefins and organosiloxanes containing ethylenically unsaturated silicon-bonded hydrocarbon groups, for example tetra-vinyl-tetramethylcyclotetrasiloxane-platinum complex (Ashby catalyst). Soluble platinum compounds that can be used include, for example, platinum-olefin complexes of the formula (PtCl2.(olefin)2 and H(PtCl3.olefin), and in this context, alkenes having 2 to 8 carbon atoms such as ethylene, propylene, isomers of butene and isomers of octene, or cycloalkanes having 5 to 7 carbon atoms such as cyclopentene, cyclohexene, and cycloheptene are preferably used. Other soluble platinum catalysts are, for example, platinum-cyclopropane complexes of the formula (PtCl2C3H6)2, reaction products of hexachloroplatinic acid with alcohols, ethers, and aldehydes, or mixtures thereof, or reaction products of hexachloroplatinic acid and / or its conversion products with vinyl-containing siloxanes such as methylvinylcyclotetrasiloxane in the presence of sodium bicarbonate in an ethanolic solution. Platinum catalysts having phosphorus and amine ligands, for example, complexes of platinum with vinylsiloxanes such as (Ph3P)2PtCl2 and sym-divinyltetramethyldisiloxane, can also be used.

[0045] Accordingly, specific examples of suitable platinum-based catalysts include (i) complexes of chloroplatinic acid with organosiloxanes containing ethylenically unsaturated hydrocarbon groups, as described in U.S. Patent No. 3,419,593, (ii) chloroplatinic acid in either the hexahydrate form or the anhydrous form, (iii) platinum-containing catalysts obtained by a method including reacting chloroplatinic acid with an aliphatic unsaturated organosilicon compound such as divinyltetramethyldisiloxane. (iv) An alkene-platinum-silyl complex described in U.S. Patent No. 6,605,734 such as (COD)Pt(SiMeCl2)2 (wherein, "COD" is 1,5-cyclooctadiene), and / or (v) A Karstedt catalyst, a platinum divinyltetramethyldisiloxane complex typically containing about 1% by weight of platinum in a vinylsiloxane polymer having a viscosity of about 200 to 750 using the test method described for component (a).

[0046] Solvents such as organic solvents like toluene have been historically used as alternatives, but the use of vinylsiloxane polymers is a much more preferred choice. These are described in U.S. Patent No. 3,715,334 and U.S. Patent No. 3,814,730. In a preferred embodiment, component (d) can be selected from coordination compounds of platinum. In one embodiment, hexachloroplatinic acid and its conversion product with vinyl-containing siloxane, Karstedt catalyst, and Speier catalyst are preferred.

[0047] Component (d) is typically present in an amount of platinum atoms providing 0.1 to 500 ppm (parts per million) based on the weight of reactive raw materials components (a) and (b). The catalyst can 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 is provided, the amount of catalyst present is in the range of 0.05 to 1.5% by weight of the composition, or 0.05 to 1.0% by weight of the composition, or 0.1 to 1.0% by weight of the composition, or 0.1 to 0.5% by weight of the composition, and the platinum catalyst is provided in a polymer masterbatch such as (a) above.

[0048] Component (e) Component (e) of the hydrosilylation-curable silicone rubber composition is R 1 -O-C(=O)-CH2CH2-S-CH2CH2-C(=O)-O-R 1 and C-(CH2OC(=O)-CH2CH2-S-R1 ) 4 (wherein each R 1 may be the same or different and is an alkyl group) and is at least one thiopropionate selected therefrom. Each R 1 alkyl may be linear, branched, and / or may contain cyclic alkyl, may contain 1 to 25 carbons, or each R 1 has 5 to 25 carbons, or each R 1 has 10 to 25 carbons, or each R 1 is a linear alkyl having 10 to 25 carbons, for example, a decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group or eicosane group.

[0049] In one embodiment, all R 1 groups in the compound of component (e) contain the same number of carbons, i.e., are the same. A small amount (less than 5 wt%, or less than 2 wt%) of branching may be present in such groups. Specific examples of component (e) include, but are not limited to, the following: (C 12 H 25 )-O-C(=O)-CH2CH2-S-CH2CH2-C(=O)-O-(C 12 H 25 ) Didodecyl 3,3'-thiodipropionate; (C 13 H 27 )-O-C(=O)-CH2CH2-S-CH2CH2-C(=O)-O-(C 13 H 27 ) Di(tridecyl) 3,3'-thiodipropionate; (C 18 H 37 )-O-C(=O)-CH2CH2-S-CH2CH2-C(=O)-O-(C 18 H 37 ) Dioctadecyl 3,3'-thiodipropionate; and C-(CH2OC(=O)-CH2CH2-S-(C 12 H 25 ))4 Pentaerythritol - tetrakis-(3-dodecyl - thio - propionate).

[0050] The above component (e) thio - propionate may be present in the composition in an amount of 0.025 - 0.5% by weight, or 0.05 - 0.35% by weight, or 0.075 - 0.35% by weight, or 0.075 - 0.25% by weight, or 0.075 - 0.20% by weight of the composition.

[0051] Optional additive Such a hydrosilylation - curable silicone rubber composition may also contain one or more optional additives according to the intended use. Examples include a curing inhibitor, a release agent, an adhesion catalyst, a peroxide, a conductive filler, a thermal conductive filler, a pot - life extender, a flame retardant, a lubricant, a heat stabilizer, a UV light stabilizer, a bactericide, a wetting agent, etc.

[0052] Curing inhibitor The curing inhibitor is used, if necessary, especially to prevent or delay the addition - reaction curing process during storage. Optional addition - reaction inhibitors for platinum - based catalysts are well - known in the art and include hydrazine, triazole, phosphine, mercaptan, organic nitrogen compounds, acetylene alcohol, silylated acetylene alcohol, maleate, fumarate, ethylenically or aromatically unsaturated amide, ethylenically unsaturated isocyanate, olefinic siloxane, unsaturated hydrocarbon mono - esters and diesters, conjugated en - in, hydroperoxide, nitrile, and diaziridine. Alkenyl - substituted siloxanes as described in U.S. Patent No. 3989667 may be used, among which cyclic methylvinylsiloxane is preferred.

[0053] One type of known hydrosilylation reaction inhibitor is the acetylene compound disclosed in U.S. Patent No. 3,445,420. Acetylenic alcohols such as 2-methyl-3-butyn-2-ol constitute a preferred type of inhibitor that suppresses the activity of platinum-containing catalysts at 25°C. Typically, compositions containing these inhibitors need to be heated at a temperature of 70°C or higher in order to cure at a practical rate.

[0054] 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 acetylenic alcohols can include these compounds having at least one silicon atom.

[0055] When present, a low inhibitor concentration of about 1 mole of inhibitor per mole of catalyst metal results in satisfactory storage stability and cure rate. In other cases, an inhibitor concentration of up to 500 moles of inhibitor per mole of catalyst metal is required. The optimal concentration for a given inhibitor in a given composition is readily determined by routine experimentation. Depending on the concentration and form in which the selected inhibitor is commercially available, when present in the composition, the inhibitor typically is present in an amount of 0.0125 to 10 wt% of the composition.

[0056] In one embodiment, the inhibitor, when present, is selected from 1-ethynyl-1-cyclohexanol (ETCH) and / or 2-methyl-3-butyn-2-ol and is present in an amount greater than 0 to 0.1 wt% of the composition.

[0057] Release agent Any suitable release agent may be used. The release agent may be, for example, a hydroxy-terminated polydimethylsiloxane having a viscosity of about 21 mPa·s at 25°C, measured using a Brookfield (trademark) rotational viscometer at 12 rpm with Spindle LV-2.

[0058] Flame retardant Examples of flame retardants include aluminum trihydrate, chlorinated paraffin, hexabromocyclododecane, melamine cyanurate, melamine polyphosphate, ammonium polyphosphate triphenyl phosphate, dimethyl methylphosphonate, tris(2,3-dibromopropyl) phosphate (brominated tris), and mixtures or derivatives thereof. When present in the composition, the flame retardant is typically present in an amount of 0.1 to 5% by weight of the composition.

[0059] Lubricant Examples of lubricants include tetrafluoroethylene, resin powder, graphite, fluorinated graphite, talc, boron nitride, fluorinated oil, silicone oil, molybdenum disulfide, a trimethylsilyl-terminated phenylmethylsiloxane dimethylsiloxane copolymer having a viscosity of 100 mPa·s to 200 mPa·s at 25°C using the viscosity test method described for component (a), and mixtures or derivatives thereof.

[0060] Heat stabilizer The compositions herein may also include one or more inorganic heat stabilizers, such as hydrated cerium oxide, cerium hydroxide, cerium carboxylate and / or cerium ester, such as cerium ethylhexanoate, hydrated aluminum oxide, red iron oxide, yellow iron oxide, carbon black, graphite and zinc oxide, used alone or in combination.

[0061] Accordingly, in one alternative, the present disclosure provides a hydrosilylation-curable silicone rubber composition comprising any suitable combination of the following components a) to e). a) One or more polyorganosiloxanes, containing at least two unsaturated groups selected from alkenyl groups and alkynyl groups per molecule, having a viscosity of 1000 mPa·s to 100,000 mPa·s at 25°C, or 5000 mPa·s to 75000 mPa·s at 25°C, or 10,000 mPa·s to 60,000 mPa·s at 25°C, and preferably present in an amount of 25 to 60% by weight of the composition, or 30 to 60% by weight of the composition, or 35 to 55% by weight of the composition. The viscosity can be measured at 25°C as described above. b) An organosilicon compound having at least two or at least three Si-H groups per molecule, and may be present in an amount of 0.1 to 10% by weight of the silicone rubber composition, or 0.1 to 7.5% by weight of the hydrosilylation-curable silicone rubber composition, or 0.5 to 7.5% by weight, or further 0.5% to 5% by weight of the composition. c) A silica reinforcing filler, preferably in a micronized form, optionally hydrophobically treated, having a high surface area, typically at least 50 m 2 / g (BET method according to ISO9277:2010). The silica reinforcing filler (c) has a surface area of 50 to 450 m 2 / g (BET method according to ISO 9277:2010), or 50 to 300 m 2 / g (BET method according to ISO 9277:2010), and is typically present in an amount of up to 40% by weight of the composition, or 1.0 to 40% by weight of the composition, or 5.0 to 35% by weight of the composition, or 10.0 to 35% by weight of the composition. d) A hydrosilylation catalyst containing or consisting of a platinum group metal or its compound, and the amount is in the range of 0.001 to 3.0% by weight of the composition, or 0.001 to 1.5% by weight of the composition, or 0.001 to 1.5% by weight, or 0.01 to 0.10% by weight of the silicone rubber composition, depending on the form / concentration in which the catalyst is provided. e) At least one thiopropionate, R 1-O-C(=O)-CH2CH2-S-CH2CH2-C(=O)-O-R 1 and C-(CH2OC(=O)-CH2CH2-S-R 1 )4 (wherein each R 1 may be the same or different and is an alkyl group), at least one thiopropionate selected therefrom. Each R 1 alkyl may be straight-chain, branched-chain, and / or may contain a cyclic alkyl group, may contain 1 to 25 carbons, or each R 1 has 5 to 25 carbons, or each R 1 has 10 to 25 carbons, or each R 1 is a straight-chain alkyl group having 10 to 25 carbons, for example, a decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group or eicosane group.

[0062] Component (e) is present in the composition in an amount of 0.025 to 0.5% by weight, or 0.05 to 0.35% by weight, or 0.075 to 0.35% by weight, or 0.075 to 0.25% by weight, or 0.075 to 0.20% by weight of the composition. Provided that the total weight% of the composition is 100% by weight.

[0063] The composition may also contain one or more of the above optional additives in the specified amounts, provided that here too, the total weight% of the composition is 100% by weight.

[0064] The above hydrosilylation-curable silicone rubber composition is usually stored before use in two or more parts. In the case of a two-part composition, the two parts are usually referred to as part (A) and part (B). (A) part typically contains a polyorganosiloxane (a) and, in the presence, a silica reinforcing filler (c), and in addition, a catalyst (d), Part (B) usually contains the crosslinking agent component (b) and, if present, an optional inhibitor and the remaining polyorganosiloxane (a) and / or silica reinforcing filler (c).

[0065] It is important that the catalyst (d) be stored separately from the crosslinking agent (b) to prevent premature curing during storage.

[0066] At least one thiopropionate, which is component (e), may be stored in either part (A) or part (B), or both, as long as it does not adversely affect the storage of any of the essential raw materials present in each part. Alternatively, if desired, component (e) may be added to the remaining composition, i.e., when the compositions of part (A) and part (B) are mixed together before use or to the combination of the compositions of part (A) and part (B) thereafter.

[0067] Any optional additives other than the inhibitors described above may be present in either part (A) or part (B), or both, as long as they do not adversely affect the storage of any of the essential raw materials present in each part.

[0068] The raw materials / components of each of part (A) and / or part (B) may be individually mixed together in their respective parts or introduced into the composition in a pre-prepared combined state, for example, to facilitate mixing of the final composition. For example, components (a) and (c) are often mixed together to form an LSR polymer base or masterbatch before introducing other raw materials. These may then be mixed with the other raw materials of the part being manufactured directly or used to produce a pre-prepared concentrate, commonly referred to in the industry as a masterbatch.

[0069] In this case, in order to facilitate the mixing of raw materials, one or more masterbatches can be utilized to successfully mix the raw materials to form the compositions of part (A) and / or part (B). For example, a "fumed silica" masterbatch can be prepared. This is, in an efficient manner, an LSR silicone rubber base containing silica reinforcing filler (c) treated in situ.

[0070] Parts A and B of the composition can be prepared by combining all of the respective components at ambient temperature. For this purpose, any mixing techniques and apparatuses described in the prior art can be used. The specific apparatus used is determined by the viscosities of the components and the final composition. Suitable mixers include, but are not limited to, a kneader mixer, a static mixer in a liquid injection molding machine, a Z-blade mixer, a two-roll mill (open mill), a three-roll mill, a Haake® Rheomix OS Lab mixer, a single-screw extruder or a twin-screw extruder, etc. Alternatively, for example, a speed mixer such as DC150.1FV, DAC400FVZ, or DAC600FVZ sold by Hauschild can be used. It may also be desirable to cool the components during mixing to avoid premature curing of the composition.

[0071] The compositions of part (A) and part (B) can be designed to be mixed in any suitable weight ratio. For example, part (A):part (B) can be mixed together at a weight ratio of 10:1 to 1:10, or 5:1 to 1:5, or 2:1 to 1:2, but most preferably, it is a weight ratio of 1:1.

[0072] Before use, the compositions of each of part (A) and part (B) are mixed together at the desired weight ratio.

[0073] The curing of the hydrosilylation-curable silicone rubber composition on the substrate is carried out, for example, in a mold, and by injection molding, for example, using a liquid injection molding system (LIMS) press molding, extrusion molding, transfer molding, press vulcanization, or calendering, a molded part can be formed. Compression set test specimens can be molded into a suitable shape, for example, a cylindrical disk with a diameter of 29.0 mm ± 0.5 mm and a thickness of 12.5 mm ± 0.5 mm, and these are compressed by 25% to a thickness of about 9.38 mm. These may be prepared in a mold or alternatively cut out from a press sheet of the silicone elastomer material.

[0074] Under compression, an LSR button (previously cured at 175 °C for 10 minutes) was held at a high temperature for an appropriate time, typically 22 hours, between two metal plates in a convection oven, then the compression was released and the test specimen was allowed to recover to a thickness close to the starting thickness to determine the compression set.

[0075] The hydrosilylation-curable silicone rubber composition is cured at any suitable temperature, for example, a temperature of 80 °C to 200 °C, or about 100 °C to 180 °C, or about 120 °C to 180 °C. As shown above, one of the standard methods for reducing compression set has historically been post-curing aimed at reducing the number of curable groups that can cure under compression during use as a gasket. Surprisingly, it has been found that the compositions defined herein do not appear to benefit from the post-curing process, as further described below.

[0076] In the case of a process for manufacturing a two-part silicone rubber composition as described above, the process comprises (i) a step of preparing a silicone-based composition containing component (a) the polymer and (c) the silica reinforcing filler, and (ii) dividing the resulting base into two parts, namely part (A) and part (B), introducing the catalyst (e) into part (A), and introducing the crosslinking agent (b) and the inhibitor (if present) into the part (B) composition. (iii) a step of introducing any other optional additives, which are other components, into either or both of part (A) and part (B); (iv) a step of storing the part (A) and part (B) compositions separately; may include.

[0077] Typically, when used, in order to avoid early curing, the part (A) and part (B) compositions are thoroughly mixed in a suitable weight ratio as described above immediately before use. Then, curing in the curing stage is carried out. The low compression set silicone elastomer compositions and methods herein are useful in applications such as acting as a barrier to prevent the absorption or penetration of air, dust, noise, liquids, gaseous substances, or dirt. Silicone elastomer materials having a low compression set as described herein may be used in gaskets. They are also utilized in a wide range of electrical applications and / or insulation applications. In the case of electrical applications, for example, the silicone elastomer materials obtained from the compositions described herein can be used as silicone coatings for standard non-silicone insulators, for example, as cable coatings for safety cables, in cable accessories such as electrical connectors, terminals, and wire seals, both for internal and external applications or for both.

[0078] They can be useful in all types of electrical applications that require wiring / cable laying / power supply, etc. For example, in the case of automotive applications, electric vehicle (EV) battery packs, EV batteries, control units within the EV, such as motor control unit (MCU) devices, lamp housings, fuse boxes, air filters, waterproof connectors, air conditioners, lighting devices, electrical connectors, terminals, and wire seals for electronic components. Other applications include those in devices designed for external waterproof applications and drip / trickle irrigation applications (for example, a micro-irrigation system that enables the slow dripping of water and nutrients to the roots of plants either from above the soil surface or buried beneath the surface).

[0079] The following examples are for illustrative purposes of the disclosure herein and are not limiting.

Example

[0080] All viscosities were measured at 25 °C unless otherwise stated. For the viscosities of the individual components in the following examples, unless otherwise stated, for viscosities exceeding 15,000 mPa·s, spindle LV-4 (a spindle LV-4 designed for viscosities in the range of 1,000 to 2,000,000 mPa·s) was used, and a Brookfield (trademark) rotational viscometer was used at an appropriate rpm. For viscosities up to 15,000 mPa·s, a cone plate configuration using cone CP-52 was used, and a Brookfield (trademark) rotational viscometer was used at an appropriate rpm for measurement.

[0081] All compression set results were guaranteed according to the industrial standard specification ISO815-1:2019 method A, where a cylindrical disk with a diameter of 29.0 ± 0.5 mm and a thickness of 12.5 mm ± 0.5 mm was compressed by 25% to a thickness of approximately 9.38 mm. Under compression, an LSR button (previously cured at 175 °C for 10 minutes) was held at a high temperature for a suitable time, typically 22 hours, between two metal plates in a convection oven, then the compression was released, and the test piece was recovered to a thickness close to the starting thickness to determine the compression set.

[0082] A series of compositions were prepared using two-part liquid silicone rubber elastomer compositions (Elas. 1 - 3) as shown in Table 1 as the standard starting compositions.

[0083]

Table 1

[0084] To avoid misunderstanding, in the examples in this specification, the compositions were prepared using component (e) added when or after the relevant (A) and (B) compositions were mixed together. In Examples 1 (Ex.1) and 2 and Comparative Examples 1 (C.1) and 2 where 0.1 wt% of a compression set additive was introduced, the cured final mixture was a combination of 49.95% of part (A) as defined in Table 1 above, 49.95% of part (B) as defined in Table 1 above, and 0.1 wt% of the compression set additive.

[0085] Similarly, in Example 5 where 0.2 wt% of CS.2 was used as the compression set additive, the cured final mixture was a combination of 49.90% of part (A) as defined in Table 1 above, 49.90% of part (B) as defined in Table 1 above, and 0.2 wt% of the compression set additive.

[0086] In the above composition, Masterbatch 1: Masterbatch 1 Using a spindle LV - 4 and measured using a Brookfield™ rotational viscometer at 6 rpm, 70.8 parts by weight of dimethylvinylsiloxy - terminated polydimethylsiloxane having a viscosity of about 53,000 mPa·s at 25°C, 22.4 parts by weight of 2 a hydrophobic fumed silica filler having a surface area of 300 m² / g, and contains. The silica is hydrophobized and does not contain vinyl functional groups.

[0087] Masterbatch 2: Masterbatch 2 Using a spindle LV - 4 and measured using a Brookfield™ rotational viscometer at 6 rpm, 66.6 parts by weight of dimethylvinylsiloxy - terminated polydimethylsiloxane having a viscosity of about 53,000 mPa·s at 25°C, 25.8 parts by weight of 2 a hydrophobic fumed silica having a surface area of 300 m² / g, and contains. The silica is hydrophobized and has about 0.178 mmol / g of vinyl functional groups.

[0088] The values of parts by weight shown are not percentage values and thus do not have to total 100.

[0089] Polymer 1: Polymer 1 is a vinyldimethyl terminated polydimethylsiloxane having a viscosity of 53,000 mPa·s at 25°C, measured using a Brookfield™ rotational viscometer at 6 rpm with a spindle LV-4.

[0090] Polymer 2: Polymer 2 is a vinyl terminated poly(dimethylsiloxane-co-methylvinylsiloxane) having a viscosity of 370 mPa·s at 25°C, measured using a Brookfield™ rotational viscometer at 12 rpm with a cone and plate configuration using a cone CP-52.

[0091] Crosslinking agent 1: Crosslinking agent 1 was a trimethyl terminated polymethylhydrogendimethylsiloxane having a viscosity of 30 mPa·s at 25°C, measured using a Brookfield™ rotational viscometer at 12 rpm with a cone and plate configuration using a cone CP-52.

[0092] Release agent: The release agent was a hydroxydimethyl terminated polydimethylsiloxane having a viscosity of about 21 mPa·s at 25°C, measured using a Brookfield™ rotational viscometer at 12 rpm with a spindle LV-2.

[0093] Cyclotetrasiloxane: The cyclotetrasiloxane was tetravinyl-tetramethyl-cyclotetrasiloxane.

[0094] Phenylmethylsiloxane copolymer: The phenylmethylsiloxane copolymer was a trimethylsilyl terminated phenylmethylsiloxane dimethylsiloxane copolymer having a viscosity of 125 mPa·s at 25°C, measured using a Brookfield™ rotational viscometer at 12 rpm with a cone and plate configuration using a cone CP-52.

[0095] CDA6: CDA6 is dodecane diol - di-(N'-salicyloyl)hydrazine, the synonym of which is 1-N',12-N'-bis(2-hydroxybenzoyl)dodecane dihydrazide, and it is commercially available from Adeka as ADK STAB™ CDA-6.

[0096] During use, the (A) part composition and the (B) part composition were mixed together at a weight ratio of 1:1. The resulting composition was inserted into a suitable mold and cured at 175 °C for 10 minutes as a button with a thickness of 12.5 mm and a diameter of 29 mm. Unless otherwise stated, the resulting silicone rubber was not post-cured. The post-cured samples were post-cured at 200 °C for 4 hours. Unless otherwise stated, all of the following compression set results were determined according to the method A of Test 815-1:2019 of the International Organization for Standardization (ISO).

[0097] Addition of compression set additives to the Elas.1 LSR composition in Table 1 Compression (compr n ) of the cured samples of Elas.1 was evaluated for compression set at several alternative temperatures over 22 hours. Ref.1 provides the compression set value that occurs when the composition of Elas.1 does not contain a compression set additive and is not post-cured.

[0098] Ref.1 (Reference Example 1)+PC is the same as the sample of Ref.1, but the sample was cured and then post-cured. Examples 1 and 2 and Comparative Examples 1 and 2 show the results of compression set for the elastomers obtained from the Elas.1 composition containing 0.1% by weight of the compression set additive present.

[0099] After hardening (and post-curing if performed), the samples were compressed and heated in an oven at 125 °C, 150 °C, 175 °C, 200 °C, or 225 °C for 22 hours. The compression applied to each sample was released after removal from the oven, and after cooling for 30 minutes, the respective compression set values were determined. The results are provided in Table 2 below.

[0100]

Table 2

[0101] CDA1 is 3-(n-salicyloyl)amino-1,2,4-triazole, the synonyms of which are 2-hydroxy-N-1H-1,2,4-triazol-3-ylbenzamide, and it is commercially available from Adeka as ADK STAB™ CDA-1.

[0102] CS.1 was C-(CH2OC(=O)-CH2CH2-S-(C 12 H 25 ))4, pentaerythritol-tetrakis-(3-dodecyl-thio-propionate).

[0103] CS.2 was (C 12 H 25 )-0-C(=O)-CH2CH2-S-CH2CH2-C(=O)-0-(C 12 H 25 ), didodecyl 3,3’-thiodipropionate.

[0104] The results for Reference Example Elas.1 at each temperature are, in effect, the expected maximum compression set values at each temperature after 22 hours of compression. The results for post-cured Elas.1 are the approximate minimum compression set values for the relevant temperatures after 22 hours of compression, although a longer post-curing period may further slightly reduce the compression set value. The results using CS.1 and CS.2 provided excellent compression set values after 22 hours of compression across all temperatures, although the initial compression across the entire temperature range of the commercially used compression set additives CDA-1 and CDA-6 was much less consistent.

[0105] An additional series of tests was conducted by adding 0.1% by weight of a compression set additive and maintaining compression at different temperatures for 168 hours instead of 22 hours as in the previous examples. The results are provided in Table 3 below.

[0106]

Table 3

[0107] To avoid the theoretical maximum compression set reaching 100%, the compression set values may exceed 100% as shown in Table 2 above. Values above 100% indicate complete compression set loss and further show the heat shrinkage effect on the relevant compression elastomer.

[0108] The results of Example 3 and Example 4 gave excellent compression set results after compression at temperatures below 200°C for 168 hours compared to Comparative Example 3 and Comparative Example 4, but did not show compression set stability at temperatures above 200°C (225°C). This indicated that the use of compression set additives CS.1 and CS.2 was overall better than CDA - 1 and CDA - 6 up to a compression temperature of about 190°C. This showed that when using CS.1 and CS.2, the compression set was improved up to a temperature of about 190°C compared to CDA - 1 and CDA - 6. Therefore, the compound specified as component (e) has been proven to be more consistently good as a compression set additive for compression set situations at temperatures from about 120°C to about 190°C.

[0109] By adding at least one thiopropionate, namely CS.1 or CS.2, as component (e) of the composition herein to the composition, it was found that the resulting cured material had significantly low compression set after compression at up to 175°C for 22 hours. Compression set was observed after compression at 200°C, but it was not overly large compared to others.

[0110] Addition of compression set additives to the Elas.2 LSR composition of Table 1 In a second series of examples, Reference Example 2 was the compression set of the cured elastomer obtained by curing the Elas.2 LSR composition described in Table 1 without a compression set additive.

[0111] In Comparative Example 5, 0.1% by weight of CDA-6 was added as a comparative compression set additive.

[0112] In Example 5, 0.2% by weight of CS-2 was added as a compression set additive, and as a result, Example 5 had only CS.2 as a compression set additive. The results of the compression set for different elastomers produced from the specified composition are shown in Table 4 below.

[0113]

Table 4

[0114] The presence of the release agent in Example 5 was found not to affect the effect of CS.2 on the compression set results of Example 5 after compression at 175 °C for 22 hours compared to CDA6. However, Example 5 gave worse results at a higher temperature of 200 °C than Comparative Example 5 (depending on CDA6). This shows that the compression set of the cured silicone elastomer in Example 5 is significantly improved here even after compression at 175 °C for 22 hours when using at least one thiopropionate, namely CS.2 instead of CDA1 and CDA6, by the component (e) of the composition herein.

[0115] Addition of the compression set additive CS.1 to the Elas.3 LSR composition of Table 1 In a third series of examples, a general-purpose LSR, Elas.3, was used. This contained 0.025 wt% CDA6 when components A and B were mixed together, and 0.05 wt% CDA6 was present in the (B) part composition before mixing. Thus, Comparative Example 6 (C.6) tested the compression set of Elas.3 alone (containing 0.025 wt% CDA6). In Example 6, Elas.3 was evaluated with an additional 0.1 wt% of CS.1. Thus, Example 6 contained 0.025 wt% CDA-6 and 0.1 wt% CS.1. The results are provided in Table 5 below.

[0116]

Table 5

[0117] Example 6 shows a further improvement in compression set when CS.1 is added to the Elas.3 composition at a level of 0.1 wt% in addition to CDA6. The addition of a small amount of tetrakis-dodecyl-thio-propionate was found to significantly reduce the compression set of the cured product of the Elas.3 composition after compression at 175 °C for 22 hours. The combination of CDA6 and CS.1 also had a significant effect on the compression set after compression at 200 °C for 22 hours.

[0118] Addition of further compression set additives to the Elas.3 LSR composition of Table 1 In a third series of examples, the general-purpose LSR, Elas.3, was also used here.

[0119] In Comparative Example 7 (C.7), the composition used was Elas.3 combined with 0.3 wt% CDA6 (i.e., when parts A and B were mixed together, the total CDA6 in the composition was 0.325 wt%).

[0120] In Example 7, the composition used was the same as C.7 with 0.1 wt% of CS.1 added.

[0121] In Example 8, the composition used was the same as C.7 with 0.3% by weight of CS.1 added.

[0122]

Table 6

[0123] The addition of a larger amount (compared with Tables 4 and 5) of CDA-6 and CS was not found to further significantly improve the compression set.

[0124] The data revealed that the addition of a small amount of 0.01 - 0.3% by weight of thio-(di)propionate significantly reduced the compression set after compression at a temperature up to about 190°C for 22 hours.

[0125] Therefore, it can be seen that the silicone elastomer material incorporating component (e) of the present specification consistently provides good compression set results up to a temperature of about 190°C without the need to take an untaking period of post-cure heating. Therefore, the silicone elastomer material is suitable for use in seal parts that require heat resistance over a long period, for example, when used as automotive seal parts and seal parts for electrical and electronic equipment.

Claims

1. A hydrosilylated curable silicone rubber composition comprising the following components, namely, a) One or more polyorganosiloxanes containing at least two unsaturated groups selected from alkenyl groups and alkynyl groups per molecule, and having a viscosity in the range of 1,000 MPa·s to 100,000 MPa·s at 25°C. b) Organosilicon compounds having at least two or at least three Si-H groups per molecule; c) A silica-reinforced filler that has been optionally hydrophobized, d) A hydrosilylation catalyst containing or consisting of a platinum group metal or a compound thereof, e) R １ -O-C(=O)-CH ２ CH ２ -S-CH ２ CH ２ -C(=O)-O-R １ and C-(CH ２ OC(=O)-CH ２ CH ２ -S-R １ ) ４ (In the formula, each R １ A hydrosilylated curable silicone rubber composition comprising at least one thiopropionate selected from (which may be the same or different, and which is an alkyl group), wherein the total weight of the composition is 100% by weight.

2. The silicone rubber composition according to claim 1, wherein at least one thiopropionate, which is component (e), is present in the composition in an amount of 0.025 to 0.5% by weight of the composition.

3. The silicone rubber composition according to claim 1 or 2, wherein at least one thiopropionate, which is component (e), is present in the composition in an amount of 0.05 to 0.35% by weight of the composition.

4. In the at least one thiopropionate which is component (e), each R １ The silicone rubber composition according to claim 1 or 2, wherein the alkyl group is a linear alkyl group having 10 to 25 carbon atoms.

5. The silicon rubber composition according to claim 1 or 2, wherein in component (e), the at least one thiopropionate comprises one or more of didodecyl 3,3'-thiodipropionate, di(tridecyl) 3,3'-thiodipropionate, dioctadecyl 3,3'-thiodipropionate, and pentaerythritol-tetrakis-(3-dodecyl-thiopropionate).

6. The silicone rubber composition according to claim 1 or 2, wherein the composition is stored in two parts, namely part (A) and part (B), before use in order to keep component (b) and component (d) separate in order to avoid premature curing.

7. The silicone rubber composition according to claim 1 or 2, wherein component (e) is present in part (A), part (B), or both parts (A) and (B) of the composition, or is added to a combination of part (A) composition and part (B) composition during or after mixing of part (A) and part (B).

8. The silicone rubber composition according to claim 1 or 2, further comprising one or more additives selected from curing inhibitors, foaming agents, mold release agents, adhesion catalysts, peroxides, conductive fillers, thermally conductive fillers, pot life extenders, flame retardants, lubricants, heat stabilizers, UV light stabilizers, bactericides, and / or wetting agents.

9. A silicone elastomer material which is a curing product of the hydrosilylated curable silicone rubber composition described in claim 1.

10. The silicone elastomer material according to claim 9, having a compression set of 25% or less, preferably 20%, after compression at 175°C for 22 hours, as measured according to Method A of the industrial standard ISO 815-1:2019, and / or a compression set of 40% or less after compression at 175°C for 168 hours, as measured according to Method A of the industrial standard ISO 815-1:2019.

11. A process for producing a silicone elastomer material, comprising the steps of: mixing a hydrosilylated curable silicone rubber composition according to claim 1 or 2; and curing the composition at a temperature of 80°C to 200°C.

12. A silicone elastomer material obtained or obtainable from a process comprising: a step of mixing a hydrosilylated curable silicone rubber composition according to claim 1 or 2; and a step of curing the composition at a temperature such that, when measured according to Method A of the industrial standard ISO 815-1:2019, it has a compression set of 25% or less, preferably 20%, after being compressed at 175°C for 22 hours from a temperature of 80°C, and / or a compression set of 40% or less after being compressed at 175°C for 168 hours, when measured according to Method A of the industrial standard ISO 815-1:2019.

13. The use of at least one thiopropionate, wherein the thiopropionate is R １ -O-C(=O)-CH ２ CH ２ -S-CH ２ CH ２ -C(=O)-O-R １ and C-(CH ２ OC(=O)-CH ２ CH ２ -S-R １ ) ４ (In the formula, each R １ The components may be the same or different, and are selected from alkyl groups, and the use is as a means to reduce the compression set in the silicone elastomer material which is the curing product of the hydrosilylated curable silicone rubber composition, and the hydrosilylated curable silicone rubber composition otherwise comprises the following components, namely, a) One or more polyorganosiloxanes containing at least two unsaturated groups selected from alkenyl groups and alkynyl groups per molecule, and having a viscosity in the range of 1,000 MPa·s to 100,000 MPa·s at 25°C. b) Organosilicon compounds having at least two or at least three Si-H groups per molecule; c) A silica-reinforced filler that has been optionally hydrophobized, d) A hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof, The use of at least one thiopropionate, the total weight percentage of the aforementioned composition being 100% by weight.

14. Use of the silicone rubber composition according to claim 1 in devices designed for external waterproofing and / or drip / tear irrigation applications in the manufacture of electrical, electronic and / or insulating applications.

15. The use according to claim 14, wherein the electrical use, the electronic use and / or the insulating use is selected from silicone coatings for non-silicone insulators, cable coatings for electrical connectors, terminals and wire seals, heat dissipation components for broadband cellular networks, and communication electronic devices.