Liquid silicone rubber composition

Abstract

The present disclosure relates to hydrosilylated (addition) curable silicone rubber compositions that, when cured, provide silicone elastomeric materials having improved low compressive deformation while avoiding the need for a post-curing step, and to a method for preparing the silicone elastomeric materials. The disclosure also extends to the use of such materials as silicone coatings in the manufacture of standard non-silicone insulators or for the manufacture of these coatings, as cable coatings, e.g. For safety cables, in cable accessories such as electrical connectors, connector seals, terminals, and wire seals, as well as in the manufacture of cable accessories such as electrical connectors, connector seals, terminals, and wire seals. The invention also relates to the use for other electrical and electronic components, in particular for the automotive industry.

Description

[0001] The present disclosure relates to hydrosilylation (addition) curable silicone rubber compositions which, when cured, provide silicone elastomeric materials having improved low compression set while avoiding a post-curing step, and to a process for preparing these silicone elastomeric materials. The invention also extends to the use of such materials in or for the manufacture of silicone coatings for standard non-silicone insulators, as cable coatings, e.g. for safety cables, in cable accessories, e.g. electrical connectors, connector seals, terminals and wire seals, and for other electrical and electronic components, in particular for the automotive industry and / or in or as hoses and gaskets for e.g. vehicle engines.

[0002] The hydrosilylation-curable silicone rubber composition contains

[0003] (i) an organopolysiloxane polymer having unsaturated (alkenyl and / or alkynyl) groups;

[0004] (ii) a compound containing silicon-bonded hydrogen atoms; and

[0005] (iii) a hydrosilylation catalyst,

[0006] These hydrosilylation-curable silicone rubber compositions are known in the art and are used to prepare silicone elastomer materials with a wide range of physical properties, including electrical insulation, heat resistance and thermal stability, frost resistance, wear resistance, flame retardancy and long-term flexibility. This unique combination of properties makes the elastomers made of liquid silicone rubber suitable for a wide range of electrical and / or insulating applications, such as those mentioned above, many of which require silicone elastomer materials to have low compression set in addition to their applications such as electrical insulation and / or thermal stability. For example, motor vehicles increasingly rely on electrical and electronic systems to achieve their full operation, even more so since the introduction of electric and hybrid vehicles. Therefore, electrical failures can lead to device failures, such as radio, light, ventilation, etc., or even damage. Many electrical connectors rely on the aforementioned silicone rubber materials to prevent electrical failures, and they need to be able to avoid failures at elevated engine temperatures.

[0007] Compression set is a key property of silicone elastomer materials used in any of the above applications. Compression set is the heat-induced fatigue behavior of silicone elastomer materials, which can be defined as the loss of the ability of the silicone elastomer material to recover to its original thickness after being compressed for a specific period of time at a set (elevated) temperature. The compression set value can be measured, for example, according to industrial standard ISO815-1:2019 method A, B or C, and determined as a percentage, so that if there is complete recovery, that is, if the thickness of the test sample is the same before and after the load is applied, the compression set value is 0%; on the contrary, if the 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 fails to fully recover to its initial shape. Without being bound by current theory, it is believed that the fundamental reason why silicone-based elastomer materials cannot recover to their original thickness after being compressed for a specified period of time at a set (elevated) temperature is that hydrosilylation-curable silicone compositions generally (if not always) do not undergo complete curing during the standard curing process. This is believed 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 crosslinker, and the hydrosilylation catalyst (most typically a platinum-based catalyst). Therefore, when the hydrosilylation-cured silicone elastomeric material is compressed at elevated temperatures, further crosslinking may occur within the silicone elastomeric material, particularly at previously unreacted Si-H positions. In addition, intermolecular bond formation may occur between polydimethylsiloxane (PDMS) chains, again particularly at previously unreacted Si-H excess positions (via hydrolysis, oxidation, or thermally induced reaction pathways), and thermal, oxidative, and thermo-oxidative rearrangements may occur within or between individual PDMS chains of the silicone elastomeric material. The occurrence of one or more of the above will result in an increase in the crosslink density within the silicone elastomeric material, and therefore a more rigid structure, which prevents the silicone elastomeric material from returning to its original thickness after compression.

[0008] Many silicone elastomer materials have significant compression set, e.g., greater than 50% or even greater than 60% compression set even after compression for a short period of 22 hours at temperatures of 125° C. and 150° C., respectively, and may suffer from problems caused by corresponding changes in shape and / or significant increases in hardness during extended use in high temperature applications unless they are subjected to a post-cure heating process. "Post-cure" is the most direct way to minimize compression set, wherein a hydrosilylation-cured silicone material is subjected to post-cure heating at a temperature of 150° C. or higher for a period of several hours (e.g., four or more hours). However, post-cure is generally not commercially desirable or indeed feasible in view of the increased energy consumption and delays in manufacturing time.

[0009] Many of the above applications generally require silicone elastomeric materials having compression set values ​​that are as low as possible, for example no more than 40%, alternatively preferably no more than 20%, after being compressed over a wide temperature range (eg, -40°C to +175°C, or even higher).

[0010] In the United States, electrical connector systems must meet the requirements of the SAE International USCAR-2 "Performance Specifications for Automotive Electrical Connector Systems" test regime. The suitability of sealed connector components within a specified temperature range is graded, with the T1 temperature grade being a temperature range of -40°C to +85°C; T2 being a temperature range of -40°C to +100°C; T3 being a temperature range of -40°C to +125°C; T3 temperature grades meeting relevant automotive specifications for a temperature range of -40°C to 125°C; T4 being a temperature range of -40°C to +150°C; and currently, the highest grade being T5 for a temperature range of -40°C to 175°C. In view of the fact that it is undesirable to force post-cure of each elastomer after curing, a variety of additives have been proposed for reducing compression set without the need for post-cure. In US5153244, the compression set value of hydrosilylation-cured silicone is significantly reduced by introducing a phthalocyanine compound or a metal derivative of such a compound (wherein the metal is copper, nickel, cobalt or iron) into the composition.

[0011] US8080598 identifies a hydrosilylation-cured silicone rubber having low compression set without post-curing with a metal deactivator selected from: diacylhydrazide-based compounds, such as dodecanediacyl-di-(N'-salicyloyl)hydrazide, a synonym of which is 1-N',12-N'-bis(2-hydroxybenzoyl)dodecanediacylhydrazide; aminotriazole-based compounds, such as 3-(n-salicyloyl)amino-1,2,4-triazole, a synonym of which is 2-hydroxy-N-1H-1,2,4-triazol-3-ylbenzamide; or aminotriazine-based compounds in combination with a cure inhibitor selected from acetylene-containing silanes, vinyl-containing low molecular weight organosiloxane compounds or alcohol derivatives having carbon-carbon triple bonds to reduce compression set. EP0517524 and US5104919 describe the use of various triazole and benzotriazole derivatives as additives for the controlled reduction of compression set of hydrosilylation-cured silicone elastomers. US5977249 describes the use of various organosulfur compounds, in particular mercaptans, and US9200146 describes the use of 3-amino-1,2,4-triazole-5-thiol bonded to silica for reducing compression set.

[0012] The present invention provides a hydrosilylation-curable silicone rubber composition, which comprises the following components:

[0013] 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;

[0014] b) organosilicon compounds having at least two, alternatively at least three Si—H groups per molecule;

[0015] c) optionally hydrophobically treated silica reinforcing fillers;

[0016] d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof;

[0017] e) at least one thiopropionate selected from the group consisting of

[0018] R 1 -OC(=O)-CH2CH2-S-CH2CH2-C(=O)-OR 1

[0019] and

[0020] C–(CH2OC(=O)–CH2CH2–SR 1 )4

[0021] Each R 1 can be the same or different and are alkyl groups, wherein the total weight % of the composition is 100 weight %.

[0022] A silicone elastomer material is also provided, which is a cured product of the above-mentioned hydrosilylation-curable silicone rubber composition, and the silicone elastomer material has a compression set of not more than 20% after compression for 22 hours at a temperature up to 190°C, measured according to industrial standard specification ISO 815-1:2019 method A.

[0023] Also provided is a method for preparing a silicone elastomer material, the method comprising the step of mixing a hydrosilylation-curable silicone rubber composition having the following components:

[0024] 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;

[0025] b) organosilicon compounds having at least two, alternatively at least three Si—H groups per molecule;

[0026] c) optionally hydrophobically treated silica reinforcing fillers;

[0027] d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof;

[0028] e) at least one thiopropionate selected from the group consisting of

[0029] R 1 -OC(=O)-CH2CH2-S-CH2CH2-C(=O)-OR 1

[0030] and

[0031] C(CH2OC(=O)–CH2CH2–SR 1 )4

[0032] Each R 1 may be the same or different and are alkyl groups; wherein the total weight % of the composition is 100 weight %;

[0033] and curing the composition at a temperature of 80°C to 200°C.

[0034] Also provided is a silicone elastomer material obtained or obtainable by a method comprising the following steps: a step of mixing a hydrosilylation-curable silicone rubber composition having the following components:

[0035] 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;

[0036] b) organosilicon compounds having at least two, alternatively at least three Si—H groups per molecule;

[0037] c) optionally hydrophobically treated silica reinforcing fillers;

[0038] d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof;

[0039] e) at least one thiopropionate selected from the group consisting of

[0040] R 1 -OC(=O)-CH2CH2-S-CH2CH2-C(=O)-OR 1

[0041] and

[0042] C–(CH2OC(=O)–CH2CH2–SR 1 )4

[0043] Each R 1may be the same or different and are alkyl groups; wherein the total weight % of the composition is 100 weight %;

[0044] and curing the composition at a temperature of 80°C to 200°C;

[0045] The silicone elastomeric material has a compression set of no greater than 20% after compression at a temperature up to 190°C for 22 hours when measured according to industry standard specification ISO 815-1:2019 Method A.

[0046] Also provided is the use of at least one thiopropionate selected from:

[0047] R 1 -OC(=O)-CH2CH2-S-CH2CH2-C(=O)-OR 1

[0048] and

[0049] C–(CH2OC(=O)–CH2CH2–SR 1 )4

[0050] Each R 1 The use is as a means of reducing compression set in a silicone elastomer material which is a cured product of a hydrosilylation-curable silicone rubber composition which further comprises the following components:

[0051] 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;

[0052] b) organosilicon compounds having at least two, alternatively at least three Si—H groups per molecule;

[0053] c) optionally hydrophobically treated silica reinforcing fillers;

[0054] d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof;

[0055] The total weight % of the composition is 100 weight %.

[0056] It has been found that compositions containing component (e) as described herein provide silicone elastomers having consistently improved (lower) compression over a wide temperature range of 100° C. to about 190° C., compared to the two most preferred commercially available compression set additives, the aforementioned dodecanedioyl-bis-(N′-salicyloyl)hydrazine (synonym 1-N′,12-N′-bis(2-hydroxybenzoyl)dodecanedihydrazide) and 3-(n-salicyloyl)amino-1,2,4-triazole (synonym 2-hydroxy-N-1H-1,2,4-triazol-3-ylbenzamide). Another advantage of using compositions containing component (e) as compression set additives over many earlier sulfur-containing compression set additives is that component (e) is not odorous, whereas other previously proposed sulfur-containing compression set additives result in the resulting silicone elastomers having a sulfur odor that is undesirable in the industry.

[0057] The components of the composition are described in more detail below.

[0058] Component (a)

[0059] 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 ranging from 1000 mPa.s to 100,000 mPa.s at 25°C.

[0060] Component (a) is a polyorganosiloxane, such as a polydiorganosiloxane, having at least two unsaturated groups per molecule, the unsaturated groups being selected from alkenyl groups or alkynyl groups. Alternatively, component (a) has at least three unsaturated groups per molecule.

[0061] The unsaturated groups of component (a) may be at terminal positions, pendant positions, or both positions.

[0062] The alkenyl group may have 2 to 30, alternatively 2 to 24, alternatively 2 to 20, alternatively 2 to 12, alternatively 2 to 10, alternatively 2 to 6 carbon atoms. Possible alkenyl groups are exemplified by, but not limited to, vinyl groups, allyl groups, methallyl groups, propenyl groups, and hexenyl groups and cyclohexenyl groups.

[0063] The alkynyl group may have 2 to 30, alternatively 2 to 24, alternatively 2 to 20, alternatively 2 to 12, alternatively 2 to 10, alternatively 2 to 6 carbon atoms. The alkynyl group may be exemplified by, but not limited to, an ethynyl group, a propynyl group, and a butynyl group.

[0064] Component (a) has a plurality of units of formula (I): R' a SiO (4-a) / 2 (I)

[0065] Wherein each R' is independently selected from aliphatic hydrocarbon groups, aliphatic non-halogenated organic groups (i.e., any aliphatic organic substituent group having one free valence at a carbon atom, regardless of the type of functional group). Saturated aliphatic hydrocarbon groups 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. Examples of unsaturated aliphatic hydrocarbon groups include, but are not limited to, the above-mentioned alkenyl groups and alkynyl groups. Aliphatic non-halogenated organic groups are exemplified by, but not limited to, suitable nitrogen-containing groups such as acylamino, imino; oxygen-containing groups (such as polyoxyalkylene groups, carbonyl groups, alkoxy groups and hydroxyl groups). Additional organic groups may include phosphorus-containing groups, boron-containing groups. The subscript "a" is 0, 1, 2 or 3, typically in this case a is mainly 2, but may contain some units where a is 1 or 3.

[0066] When R' is an alkyl group as described above, alternatively, a methyl group, the siloxy units may be described by the shorthand nomenclature, i.e. - "M", "D", "T" and "Q". The M unit corresponds to a siloxy unit with a = 3, i.e. R'3SiO 1 / 2 ; The D unit corresponds to a = 2 siloxy unit, that is, R'2SiO 2 / 2 ; T unit corresponds to a = 1 siloxy unit, that is, R'1SiO 3 / 2 ; Q unit corresponds to a = 0 silicon oxygen unit, that is, SiO 4 / 2 Polyorganosiloxanes such as the polydiorganosiloxane of component (a) are substantially linear but may contain a certain proportion of branches due to the presence of T units (as described previously) within the molecule, so that the average value of subscript a in structure (i) is about 2.

[0067] Examples of typical R' groups on the one or more polyorganosiloxanes of component (a) containing at least two unsaturated groups selected from alkenyl groups and alkynyl groups per molecule mainly include alkyl groups, especially methyl and ethyl, alternatively methyl groups, but in addition to the required at least two unsaturated groups selected from alkenyl groups and / or alkynyl groups (usually alkenyl groups), aryl groups and / or fluoroalkyl groups, such as trifluoropropyl groups or perfluoroalkyl groups, may also be included. These groups may be in side chain positions (on D or T siloxy units) or may be in terminal positions (on M siloxy units).

[0068] Therefore, the polymer chain of component (a) can be selected from polydimethylsiloxane, alkylmethylpolysiloxane, alkylarylpolysiloxane or their copolymers (wherein mentioning alkyl means any suitable alkyl group, alternatively has an alkyl group of two or more carbons), provided that each component (a) polymer comprises at least two alkenyl groups and / or alkynyl groups, typically at least two alkenyl groups. Such polymer chains can have any suitable terminal groups, for example, they can be trialkyl end-capped, alkenyldialkyl end-capped, alkynyldialkyl end-capped, or can be end-capped with any other suitable terminal group combination, provided that each polymer contains at least two unsaturated groups selected from alkenyl groups and alkynyl groups per molecule. In one embodiment, the terminal groups of such polymers do not include any silanol terminal groups.

[0069] Thus, for example, component (a) may be:

[0070] Dialkyl alkenyl terminated polydimethylsiloxanes, such as dimethylvinyl terminated polydimethylsiloxanes; dialkyl alkenyl terminated dimethylmethylphenylsiloxanes, such as dimethylvinyl terminated dimethylmethylphenylsiloxanes; trialkyl terminated dimethylmethylvinyl polysiloxanes; dialkyl vinyl terminated dimethylmethylvinyl polysiloxane copolymers; dialkyl vinyl terminated methylphenyl polysiloxanes, dialkyl alkenyl terminated methylvinylmethylphenylsiloxanes; dialkyl alkenyl terminated methylvinyldiphenylsiloxanes; dialkyl alkenyl terminated methylvinylmethylphenyldimethylsiloxanes; trimethyl terminated methylvinylmethylphenylsiloxanes; trimethyl terminated methylvinyldiphenylsiloxanes; or trimethyl terminated methylvinylmethylphenyldimethylsiloxanes.

[0071] Component a) has a viscosity of 1000 to 100,000 mPa.s at 25°C, alternatively 5000 to 75,000 mPa.s at 25°C, 10,000 to 60,000 mPa.s at 25°C, and is preferably present in an amount of 25 to 60 wt% of the composition, alternatively 30 to 60 wt% of the composition, alternatively 35 to 55 wt% of the composition. Viscosity may be increased at 25°C using a Brookfield with spindle LV-4 for viscosities exceeding 15,000 mPa.s. TM A rotational viscometer (spindle LV-4 designed for viscosities in the range between 1,000 mPa.s and 2,000,000 mPa.s) was measured at appropriate rpm, and for viscosities up to 15,000 mPa.s at 25°C and appropriate rpm a Brookfield with cone and plate arrangement with cone CP-52 was used. TM Rotational viscometer measurement.

[0072] Component (b)

[0073] Component (b) is used as a crosslinking agent and is provided in the form of an organosilicon compound having at least two, alternatively at least three Si-H groups per molecule. Component (b) typically contains three or more silicon-bonded hydrogen atoms, so that the hydrogen atoms can react with the unsaturated olefinic and / or alkynyl groups of component (a) to form a network structure therewith and thereby cure the composition. When polymer (a) has more than two unsaturated groups per molecule, some or all of component (b) may alternatively have two silicon-bonded hydrogen atoms per molecule.

[0074] The molecular configuration of the organosilicon compound (b) having at least two, alternatively at least three Si-H groups per molecule is not particularly limited. It may be a straight chain, a branched chain (a straight chain having some branches due to the presence of a T group), a cyclic chain, or a silicone resin-based polyorganosiloxane.

[0075] Although the molecular weight of component (b) is not particularly limited, the viscosity is generally from 5 mPa.s to 50,000 mPa.s at 25°C using the test method as described for component (a).

[0076] The silicon-bonded organic group used in component (b) can be exemplified by: alkyl groups such as methyl, ethyl, propyl, n-butyl, tert-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, preferably alkyl groups having 1 to 6 carbons, in particular methyl, ethyl or propyl or phenyl. Preferably, the silicon-bonded organic group used in component (b) is an alkyl group, alternatively methyl, ethyl or propyl.

[0077] Examples of organosilicon compounds (b) having at least two, alternatively at least three Si-H groups per molecule include, but are not limited to:

[0078] (a') trimethylsiloxy-terminated methylhydrogenpolysiloxane,

[0079] (b') trimethylsiloxy-terminated polydimethylsiloxane-methylhydrogensiloxane,

[0080] (c') a dimethylsiloxane-methylhydrogensiloxane copolymer terminated with dimethylhydrogensiloxy groups,

[0081] (d') dimethylsiloxane-methylhydrogensiloxane cyclic copolymer,

[0082] (e') from (CH3)2HSiO1 / 2 Unit, (CH3)3SiO1 / 2 Unit and SiO 4 / 2 Unit composed of copolymers and / or silicone resins,

[0083] (f') from (CH3)2HSiO1 / 2 Unit and SiO 4 / 2 Unit composed of copolymers and / or silicone resins,

[0084] (g') a methylhydrogensiloxane cyclic homopolymer having 3 to 10 silicon atoms per molecule;

[0085] Alternatively, component (b) the crosslinking agent may be a filler, such as silica treated with one of the above-mentioned substances, and mixtures thereof.

[0086] In one embodiment, component (b) is selected from methylhydrogenpolysiloxane terminated with trimethylsiloxy groups at both molecular ends; copolymers of methylhydrogensiloxane and dimethylsiloxane terminated with trimethylsiloxy groups at both molecular ends; dimethylsiloxane terminated with dimethylhydrogensiloxane at both molecular ends; copolymers of methylhydrogensiloxane and dimethylsiloxane terminated with dimethylhydrogensiloxy groups at both molecular ends.

[0087] 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 from 0.5:1 to 10:1. When the ratio is less than 0.5:1, a well-cured composition is not obtained. When the ratio exceeds 10:1, there is a tendency for the cured composition to increase in hardness when heated. Preferably, the amount of component (b) is such that the molar ratio of silicon-bonded hydrogen atoms of component (ii) to alkenyl / alkynyl groups, alternatively alkenyl groups, of component (a) is in the range of 0.7:1.0 to 5.0:1.0, alternatively 0.9:1.0 to 2.5:1.0, and further alternatively 0.9:1.0 to 2.0:1.0.

[0088] The silicon-bonded hydrogen (Si-H) content of component (b) is determined using quantitative infrared analysis according to ASTM E168. In this case, when relying on a hydrosilylation cure process, the ratio of silicon-bonded hydrogen to alkenyl (vinyl) and / or alkynyl groups is important. Generally speaking, this is determined by calculating the total weight % of alkenyl (e.g., vinyl) [V] in the composition and the total weight % of silicon-bonded hydrogen [H] in the composition, and assuming that 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].

[0089] Typically, component (b) will be present in an amount of from 0.1% to 10% by weight of the hydrosilylation-curable silicone rubber composition, alternatively from 0.1% to 7.5% by weight of the hydrosilylation-curable silicone rubber composition, alternatively from 0.5% to 7.5% by weight of the hydrosilylation-curable silicone rubber composition, further alternatively from 0.5% to 5% by weight of the hydrosilylation-curable silicone rubber composition, depending on the number of unsaturated groups in component (a) and the number of Si-H groups in component (b).

[0090] Component (c)

[0091] 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 an alternative, the fumed silica, precipitated silica and / or colloidal silica are provided in a finely divided form.

[0092] Precipitated silica, fumed silica and / or colloidal silica are preferred because of their relatively high surface areas (particularly when provided in finely divided form, typically at least 50 m 2 / g (BET method according to ISO 9277:2010)), so they are particularly preferred. Typically, materials with a surface area of ​​50 to 450 m 2 / g (according to BET method of ISO 9277:2010), alternatively 50 to 300 m 2 / g (BET method according to ISO 9277:2010) of filler. All these types of silica are commercially available.

[0093] When the silica reinforcing filler (c) has natural hydrophilicity (e.g., untreated silica filler), it is usually treated with a treating agent to impart hydrophobicity. These surface-modified silica reinforcing fillers (c) do not agglomerate and can be uniformly incorporated into the polydiorganosiloxane polymer (a) described below because the surface treatment makes the filler easily wetted by component (a).

[0094] In general, the silica reinforcing filler (c) may be surface treated with any low molecular weight silicone compound disclosed in the art to be suitable for preventing wrinkling of the liquid silicone rubber (LSR) composition during processing, for example, organosilanes, polydiorganosiloxanes or organosilazanes, such as hexaalkyldisilazane, short chain siloxane diols, to render the silica reinforcing filler (c) hydrophobic and thus easier to handle and obtain a homogeneous mixture with the other ingredients. Specific examples include, but are not limited to, silanol terminated trifluoropropylmethylsiloxane, silanol terminated vinylmethyl (ViMe) siloxane, silanol terminated methylphenyl (MePh) siloxane, liquid hydroxydimethyl terminated polydiorganosiloxanes containing an average of 2 to 20 repeating units of diorganosiloxane per molecule, hydroxydimethyl terminated phenylmethylsiloxane, hexaorganodisiloxanes such as hexamethyldisiloxane, divinyltetramethyldisiloxane; hexaorganodisilazanes such as hexamethyldisilazane (HMDZ), divinyltetramethyldisilazane and tetramethylbis(trifluoropropyl)disilazane; hydroxydimethyl terminated polydimethylmethylvinylsiloxane, octamethylcyclotetrasiloxane and silanes including, but not limited to, methyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, trimethylchlorosilane, dimethyldichlorosilane, trichloromethylsilane.

[0095] In one embodiment, the treating agent may be selected from silanol terminated vinylmethyl (ViMe) siloxanes, liquid hydroxydimethyl terminated polydiorganosiloxanes containing an average of 2 to 20 diorganosiloxane repeating units per molecule, hexaorganodisiloxanes such as hexamethyldisiloxane, divinyltetramethyldisiloxane; hexaorganodisilazanes such as hexamethyldisilazane (HMDZ), divinyltetramethyldisilazane; and hydroxydimethyl terminated polydimethylmethylvinylsiloxane, octamethylcyclotetrasiloxane and silanes including but not limited to methyltriethoxysilane, dimethyldiethoxysilane and / or vinyltriethoxysilane. A small amount of water may be added along with the silica treating agent as a processing aid.

[0096] The surface treatment of the untreated silica reinforcing filler (c) can be performed prior to introduction into the composition or in situ (i.e., in the presence of at least a portion of the other ingredients of the composition herein, by blending the ingredients together at room temperature or above until the filler is completely treated). Typically, the untreated silica reinforcing filler (c) is treated in situ with a treating agent in the presence of component (a), which results in the preparation of a silicone rubber matrix material that can subsequently be mixed with the other ingredients.

[0097] Silica reinforcing filler (c) is optionally present in an amount up to 40 wt. % of the composition, alternatively 1.0 wt. % to 40 wt. % of the composition, alternatively 5.0 wt. % to 35 wt. % of the composition, alternatively 10.0 wt. % to 35 wt. % of the composition.

[0098] Component (d)

[0099] The component (d) of the composition is a hydrosilylation catalyst comprising or consisting of a platinum group metal or its compound. These catalysts are generally selected from catalysts of platinum group metals (platinum, ruthenium, osmium, rhodium, iridium and palladium), or compounds of one or more metals in such metals. Alternatively, due to the high activity level of these catalysts in the hydrosilylation reaction, platinum and rhodium compounds are preferred, with platinum compounds being the most preferred. In the hydrosilylation (or addition) reaction, a hydrosilylation catalyst such as component (d) herein catalyzes the reaction between an unsaturated group (generally an alkenyl group, for example, a vinyl group) and a Si-H group.

[0100] The catalyst (d) may be a platinum group metal, a platinum group metal deposited on a carrier such as activated carbon, a metal oxide such as alumina or silica, silica gel or charcoal powder, or a compound or complex of a platinum group metal. Preferably the platinum group metal is platinum.

[0101] 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, such as hexachloroplatinic acid (Pt oxidation state IV) (Speier catalyst), chloroplatinic acid in solution in alcohols, such as isooctyl 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, such as tetravinyltetramethylcyclotetrasiloxane-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), in this context preferably using olefins 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. Other soluble platinum catalysts are, for example, platinum-cyclopropane complexes of 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 (e.g., methylvinylcyclotetrasiloxane) in the presence of an ethanolic solution containing sodium bicarbonate. Platinum catalysts with phosphorus and amine ligands, such as (Ph3P)2PtCl2, and complexes of platinum with vinyl siloxanes, such as symmetrical divinyltetramethyldisiloxane, can also be used.

[0102] Thus, specific examples of suitable platinum-based catalysts include:

[0103] (i) complexes of chloroplatinic acid and organosiloxanes containing ethylenically unsaturated hydrocarbon groups as described in US Pat. No. 3,419,593;

[0104] (ii) chloroplatinic acid in the form of hexahydrate or in anhydrous form;

[0105] (iii) a platinum-containing catalyst obtained by a process comprising the steps of: reacting chloroplatinic acid with an aliphatically unsaturated organosilicon compound such as divinyltetramethyldisiloxane;

[0106] (iv) olefin-platinum-silyl complexes such as (COD)Pt(SiMeCl2)2 as described in U.S. Pat. No. 6,605,734, wherein "COD" is 1,5-cyclooctadiene; and / or

[0107] (v) Karstedt's catalyst, a platinum divinyltetramethyldisiloxane complex, typically containing about 1 wt % platinum in a vinyl siloxane polymer having a viscosity of about 200 to 750 using the test method as described for component (a).

[0108] Solvents such as toluene and similar organic solvents have historically been used as alternatives, but the use of vinyl siloxane polymers is by far the preferred choice. These are described in US 3,715,334 and US 3,814,730. In a preferred embodiment, component (d) may be selected from coordination compounds of platinum. In one embodiment, hexachloroplatinic acid and its conversion products with vinyl-containing siloxanes, Karstedt catalysts and Speier catalysts are preferred.

[0109] Component (d) is typically present in an amount providing 0.1 ppm to 500 ppm (parts per million) of platinum atoms relative to the weight of the reactive ingredients, i.e., components (a) and (b). The catalyst may be added as a single substance or as a mixture of two or more different substances. Typically, depending on the form / concentration in which the catalyst is provided, the amount of the catalyst present will be in the range of 0.05 wt % to 1.5 wt %, alternatively 0.05 wt % to 1.0 wt %, alternatively 0.1 wt % to 1.0 wt %, alternatively 0.1 wt % to 0.5 wt % of the composition, wherein the platinum catalyst is provided in a masterbatch of a polymer (such as (a) described above).

[0110] Component (e)

[0111] Component (e) of the hydrosilylation-curable silicone rubber composition is at least one thiopropionate selected from the following:

[0112] R 1 -OC(=O)-CH2CH2-S-CH2CH2-C(=O)-OR 1

[0113] and

[0114] C–(CH2OC(=O)–CH2CH2–SR 1 )4

[0115] Each R 1 can be the same or different and are alkyl groups. 1 The alkyl group may be linear, branched and / or may contain cyclic alkyl groups and may contain from 1 to 25 carbon atoms, alternatively each R 1 having 5 to 25 carbon atoms, alternatively each R 1 having 10 to 25 carbon atoms, alternatively each R 1 is a straight-chain alkyl group having 10 to 25 carbons, for example, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group or an eicosyl group.

[0116] In one embodiment, all R 1 The groups contain the same number of carbons, i.e. are identical. A small amount (less than 5 wt %, alternatively less than 2 wt %) of branching may be present in such groups. Specific examples of component (e) include, for example purposes, but are not limited to

[0117] (C 12 H 25 )-OC(=O)-CH2CH2-S-CH2CH2-C(=O)-O-(C 12 H 25 )

[0118] Didodecyl 3,3'-thiodipropionate;

[0119] (C 13 H 27 )-OC(=O)-CH2CH2-S-CH2CH2-C(=O)-O-(C 13 H 27 )

[0120] 3,3'-Di(tridecyl)thiodipropionate;

[0121] (C 18 H 37 )-OC(=O)-CH2CH2-S-CH2CH2-C(=O)-O-(C 18 H 37 )

[0122] Distearyl 3,3'-thiodipropionate; and

[0123] C–(CH2OC(=O)–CH2CH2–S-(C 12 H 25 ))4

[0124] Pentaerythritol-tetrakis-(3-dodecylthiopropionate)

[0125] Component (e) The thiopropionic acid ester as described above may be present in the composition in an amount of 0.025% to 0.5%, alternatively 0.05% to 0.35%, alternatively 0.075% to 0.35%, alternatively 0.075% to 0.25%, alternatively 0.075% to 0.20% by weight of the composition.

[0126] Optional additives

[0127] Depending on the intended use, such hydrosilylation-curable silicone rubber compositions may also contain one or more optional additives. Examples include curing inhibitors, mold release agents, adhesion catalysts, peroxides, conductive fillers, thermal conductive fillers, pot life extenders, flame retardants, lubricants, heat stabilizers, UV light stabilizers, bactericides, wetting agents, etc.

[0128] Curing inhibitor

[0129] When needed, use curing inhibitor to prevent or delay the addition reaction curing process, especially during storage.The optional addition reaction inhibitor based on the catalyst of platinum is well known in the art and includes hydrazine, triazole, phosphine, mercaptan, organic nitrogen compound, alkynol, methane silylation alkynol, maleate, fumarate, ethylenic or aromatic unsaturated amide, ethylenic unsaturated isocyanate, olefinic siloxane, unsaturated hydrocarbon monoester and diester, conjugated alkene-alkynes, hydroperoxide, nitrile and diaziridine.Can use the siloxane of alkenyl replacement as described in US3989667, wherein preferred cyclic methyl vinyl siloxane.

[0130] One class of known hydrosilylation reaction inhibitors are the acetylenic compounds disclosed in US 3445420. Alkynols such as 2-methyl-3-butyn-2-ol constitute a class of preferred inhibitors which will inhibit the activity of platinum-containing catalysts at 25° C. Compositions containing these inhibitors generally require heating at temperatures of 70° C. or above in order to cure at an achievable rate.

[0131] Examples of alkynols 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-pentene-4-yn-3-ol, and mixtures thereof. Alkynol derivatives may include those compounds having at least one silicon atom.

[0132] When present, inhibitor concentrations as low as 1 mole inhibitor per mole of catalyst metal will in some cases impart satisfactory storage stability and cure rates. In other cases, inhibitor concentrations of up to 500 moles inhibitor per mole of catalyst metal are required. The optimum concentration of a given inhibitor in a given composition is readily determined by routine experimentation. When present in the composition, the inhibitor is typically present in an amount of 0.0125% to 10% by weight of the composition, depending on the concentration and form in which the selected inhibitor is provided / commercially available.

[0133] In one embodiment, when present, the inhibitor is selected from 1-ethynyl-1-cyclohexanol (ETCH) and / or 2-methyl-3-butyn-2-ol and is present in an amount from greater than zero to 0.1% by weight of the composition.

[0134] Release agent

[0135] Any suitable mold release agent may be utilized. For example, it may be a hydroxydimethyl terminated polydimethylsiloxane having a viscosity of about 21 mPa.s at 25°C, which is measured using a Brookfield with spindle LV-2. TM The rotational viscometer was measured at 12 rpm.

[0136] Flame retardants

[0137] Examples of flame retardants include aluminum trihydrate, chlorinated paraffin, hexabromocyclododecane, melamine cyanurate, melamine phosphate, ammonium polyphosphate, triphenyl phosphate, dimethyl methylphosphonate, tris(2,3-dibromopropyl)phosphate (tribromide), 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.

[0138] Lubricants

[0139] Examples of lubricants include tetrafluoroethylene, resin powder, graphite, fluorinated graphite, talc, boron nitride, fluorinated oil, silicone oil, molybdenum disulfide, trimethylsilyl-terminated phenylmethylsiloxane dimethylsiloxane copolymers having a viscosity of 100 to 200 mPa.s at 25° C. using the viscosity test method as described for component (a), and mixtures or derivatives thereof.

[0140] Heat Stabilizer

[0141] The composition herein may further comprise one or more inorganic heat stabilizers, used alone or in combination, such as hydrated cerium oxide, cerium hydroxide, cerium carboxylates and / or cerium esters, such as cerium ethylhexanoate, hydrated aluminum oxide, red iron oxide, yellow iron oxide, carbon black, graphite and zinc oxide.

[0142] Therefore, in an alternative, the present disclosure therefore provides a hydrosilylation-curable silicone rubber composition comprising any suitable combination of the following components:

[0143] a) one or more polyorganosiloxanes containing at least two unsaturated groups per molecule selected from alkenyl groups and alkynyl groups and having a viscosity in the range of 1000 to 100,000 mPa.s at 25°C; alternatively 5000 to 75,000 mPa.s at 25°C, 10,000 to 60,000 mPa.s at 25°C, preferably present in an amount of 25 to 60% by weight of the composition, alternatively 30 to 60% by weight of the composition, alternatively 35 to 55% by weight of the composition. The viscosity may be measured at 25°C as described above.

[0144] b) an organosilicon compound having at least two, alternatively at least three Si-H groups per molecule, which may be present in an amount of 0.1 to 10 wt % of the silicone rubber composition, alternatively 0.1 to 7.5 wt % of the hydrosilylation-curable silicone rubber composition, alternatively 0.5 to 7.5 wt % of the composition, further alternatively 0.5 to 5 wt %.

[0145] c) silica reinforcing fillers, preferably in finely divided form and optionally hydrophobically treated;

[0146] High surface area, which is usually at least 50m 2 / g (according to BET method of ISO 9277:2010). The silica reinforcing filler (c) has 50m 2 / g to 450m 2 / g(according to ISO

[0147] 9277:2010 BET method), alternatively 50m 2 / g to 300m 2 / g(according to ISO

[0148] 9277:2010) and is typically present in an amount of up to 40 wt % of the composition, alternatively 1.0 wt % to 40 wt % of the composition, alternatively 5.0 wt. % to 35 wt. % of the composition, alternatively 10.0 wt. % to 35 wt. % of the composition;

[0149] d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; in an amount, depending on the form / concentration in which the catalyst is provided, of 0.001 wt % to 3.0 wt % of the composition, alternatively 0.001 wt % to 1.5 wt % of the composition, alternatively 0.01 wt % to 1.5 wt % of the composition, alternatively 0.01 wt % to 0.01 wt % of the silicone rubber composition

[0150] to 0.1.0 wt %.

[0151] e) at least one thiopropionate selected from the group consisting of

[0152] R 1 -OC(=O)-CH2CH2-S-CH2CH2-C(=O)-OR 1

[0153] and

[0154] C–(CH2OC(=O)–CH2CH2–SR 1 )4

[0155] Each R 1 can be the same or different and are alkyl groups. 1 The alkyl group may be linear, branched and / or may contain cyclic alkyl groups and may contain from 1 to 25 carbon atoms, alternatively each R 1 having 5 to 25 carbon atoms, alternatively each R 1 having 10 to 25 carbon atoms, alternatively each R 1 is a straight-chain alkyl group having 10 to 25 carbons, for example, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group or an eicosyl group.

[0156] Component (e) is present in the composition in an amount of 0.025 wt % to 0.5 wt %, alternatively 0.05 wt % to 0.35 wt %, alternatively 0.075 wt % to 0.35 wt %, alternatively 0.075 wt % to 0.25 wt %, alternatively 0.075 wt % to 0.20 wt % of the composition.

[0157] Provided that the total weight % of the composition is 100 weight %.

[0158] The composition may also contain one or more of the abovementioned optional additives in the amounts again indicated, provided that the total weight % of the composition is 100 weight %.

[0159] The above hydrosilylation-curable silicone rubber composition is usually stored in two or more parts before use. In the case of a two-part composition, the two parts are usually referred to as part (A) and part (B):

[0160] In addition to the polyorganosiloxane (a) and the filler (c) (when present), part (A) generally contains a catalyst (d), and

[0161] Part (B) generally comprises the crosslinker component (b), and, when present, optionally an inhibitor and the remainder of the polyorganosiloxane (a) and / or silica reinforcing filler (c).

[0162] It is important to store the catalyst (d) separately from the crosslinking agent (b) to prevent premature curing during storage.

[0163] Component (e) at least one thio-propionic acid ester may be stored in part (A) or part (B) or in both parts, provided that they do not negatively affect the storage of any essential ingredients present in the respective parts. Alternatively, if desired, component (e) may be added to the remaining composition, i.e., to the combination of the part (A) and part (B) compositions, during or after mixing the part (A) composition and the part (B) composition together before use.

[0164] Any optional additives other than the inhibitors described above may be incorporated in either part (A) or part (B) or in both parts, provided that they do not adversely affect the storage of any essential ingredients present in the respective parts.

[0165] The ingredients / components in each of part (A) and / or part (B) may be mixed together individually in the corresponding parts, or may be introduced into the composition in a pre-made combined form, for example to facilitate mixing of the final composition. For example, components (a) and (c) are typically mixed together to form an LSR polymer base or masterbatch before the other ingredients are introduced. These may then be mixed with the other ingredients of the directly prepared part, or may be used to prepare a pre-made concentrate commonly referred to in the industry as a masterbatch.

[0166] In this case, one or more masterbatches may be used to successfully mix the ingredients to form the part (A) and / or part (B) compositions in order to facilitate mixing of the ingredients. For example, a "fumed silica" masterbatch may be prepared. This is essentially an LSR silicone rubber base with an in-situ treated silica reinforcing filler (c).

[0167] Parts A and B of the composition can be prepared by combining all of their respective components at ambient temperature. Any mixing technique and apparatus described in the prior art can be used for this purpose. The specific apparatus to be used will depend on the components and the viscosity of the final composition. Suitable mixers may include, but are not limited to, kneading mixers, static mixers in liquid injection molding machines, Z-blade mixers, two-roll mills (open mills), three-roll mills, Rheomix OS Lab mixer, screw extruder or twin screw extruder etc. A high speed mixer such as sold by, for example, Hauschild and as DC 150.1FV, DAC 400FVZ or DAC 600FVZ may alternatively be used. It may be desirable to cool the components during mixing to avoid premature solidification of the composition.

[0168] The part (A) and part (B) compositions can be designed to be mixed in any suitable weight ratio, for example, part (A): part B can be mixed together in a weight ratio of 10:1 to 1:10, or 5:1 to 1:5, or 2:1 to 1:2, but a weight ratio of 1:1 is most preferred.

[0169] Prior to use, the respective Part (A) and Part (B) compositions are mixed together in the desired weight ratio.

[0170] The curing of the hydrosilylation-curable silicone rubber composition on the substrate can be carried out, for example, in a mold to form a molded part by injection molding using, for example, a liquid injection molding system (LIMS) compression molding, extrusion molding, transfer molding, pressurized vulcanization, or calendaring. Compression set test pieces can be molded into suitable shapes, such as cylindrical disks with a diameter of 29.0 mm ± 0.5 mm and a thickness of 12.5 mm ± 0.5 mm, and they are compressed 25% to a thickness of about 9.38 mm. These test pieces can be prepared in a mold, or alternatively can be cut out from a pressed sheet of silicone elastomer material.

[0171] The LSR buttons (previously cured at 175°C for 10 minutes) are held between two metal plates in a convection oven under compression for a suitable period of time, typically 22 hours at elevated temperature, after which the compression is released and the test piece is allowed to recover to a thickness close to the starting thickness, thereby allowing the compression set to be determined.

[0172] The hydrosilylation-curable silicone rubber composition is cured at any suitable temperature, for example, at a temperature of 80°C to 200°C, alternatively about 100°C to 180°C, alternatively about 120°C to 180°C. As indicated above, one of the standard methods for reducing compression set has historically been post-curing, with the goal of reducing the number of curable groups that may cure under compression during use as a gasket. It has been surprisingly found that the composition as defined herein does not appear to benefit from a post-curing process, as will be further explained below.

[0173] As for the method of manufacturing the two-part silicone rubber composition as described above, the method may include the following steps:

[0174] (i) preparing a silicone base composition comprising components (a) a polymer and (c) a silica reinforcing filler,

[0175] (ii) The resulting base is divided into two parts, part (A) and part (B), and the catalyst (d) is introduced into the part (A), and the crosslinking agent (b) and the inhibitor (if any) are introduced into the part (B) composition.

[0176] (iii) introducing other components and any other optional additives into either or both of part (A) and part (B); and

[0177] (iv) storing the Part (A) and Part (B) compositions separately.

[0178] Typically, when used, part (A) and part (B) compositions are fully mixed in a suitable weight ratio as described above, and fully mixed immediately before use to avoid premature curing. Then the curing stage is cured. The low compression set silicone elastomer composition and method herein can be used for applications, such as acting as a barrier to prevent the absorption or penetration of air, dust, noise, liquid, gaseous matter or dirt. Silicone elastomer materials with low compression set as described herein can be used for pads. They are also used in electrical and / or insulating applications of a wide range. In the case of electrical applications, for example, the silicone elastomer materials produced by the composition described herein can be used in internal and external applications or for both internal and external applications, for example as silicone coatings for standard non-silicone insulators, as cable coatings for example safety cables, for cable accessories such as electrical connectors, terminals and wire seals.

[0179] They can be used in various electrical applications that require wiring / cables / power supplies, etc. For example, in the case of automotive applications, they include electrical connectors, terminals, and wire seals for electric vehicle (EV) battery packs, EV batteries, control units in EVs (e.g., in motor control unit (MCU) devices), lamp housings, fuse boxes, air filters, waterproof connectors, air conditioners, lighting devices, electronic components, and other applications include exterior waterproofing applications and equipment designed for drip irrigation / drip irrigation applications (e.g., micro-irrigation systems that allow water and nutrients to drip slowly from above the soil surface or buried below the surface to the roots of plants).

[0180] The following examples are intended to illustrate but not to limit the disclosure herein. Example

[0181] Unless otherwise specified, all viscosities are measured at 25° C. Unless otherwise specified, the viscosities of the various components in the following examples were measured using a Brookfield 1000 with spindle LV-4 for viscosities exceeding 15,000 mPa.s. TMA rotational viscometer (spindle LV-4 designed for viscosities in the range of 1,000 mPa.s to 2,000,000 mPa.s) was measured at appropriate rpm, and for viscosities up to 15,000 mPa.s a Brookfield with cone and plate arrangement with cone CP-52 was used at appropriate rpm. TM Rotational viscometer measurement.

[0182] All compression set results were conducted according to industry standard specification ISO 815-1:2019 Method A, where a cylindrical disk of 29.0 mm ± 0.5 mm diameter and 12.5 mm ± 0.5 mm thickness was compressed 25% to about 9.38 mm thickness. Under compression, the LSR buttons (previously cured at 175°C for 10 minutes) were held between two metal plates in a convection oven for a suitable period of time, typically 22 hours at elevated temperature, after which the compression was released and the test piece was allowed to recover to a thickness close to the starting thickness, allowing the compression set to be determined.

[0183] A series of compositions were prepared using the 2-part liquid silicone rubber elastomer compositions (Elas. 1-3) as shown in Table 1 as standard starting compositions.

[0184] Table 1: 2-part liquid silicone rubber (LSR) elastomer compositions (Elas. 1–3)

[0185]

[0186] For the avoidance of doubt, in the examples herein, the compositions are prepared by adding component (e) during or after mixing together the relevant Part (A) and Part (B) compositions. Thus, in Ex. 1 and 2 and C. 1 and 2, where 0.1 wt. % of the compression set additive is introduced, the cured final mixture is a combination of 49.95% Part (A) as defined in Table 1 above, 49.95% Part (B) as defined in Table 1 above, together with 0.1 wt. % of the compression set additive.

[0187] Similar to Example 5 where 0.2 wt% 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, together with 0.2 wt% of the compression set additive.

[0188] In the above composition:

[0189] Masterbatch 1: Masterbatch 1 contains:

[0190] 70.8 parts by weight of dimethylvinylsiloxy terminated polydimethylsiloxane having a viscosity of about 53,000 mPa.s at 25° C., the viscosity being measured using a Brookfield with spindle LV-4 TM The rotational viscometer was measured at 6 rpm, and

[0191] The surface area of ​​22.4 parts by weight is about 300m 2 / g of fumed silica filler. The silica is hydrophobized and does not contain vinyl functional groups;

[0192] Masterbatch 2: Masterbatch 2 contains:

[0193] 66.6 parts by weight of dimethylvinylsiloxy terminated polydimethylsiloxane having a viscosity of about 53,000 mPa.s at 25° C., the viscosity being measured using a Brookfield with spindle LV-4 TM The rotational viscometer was measured at 6 rpm, and

[0194] The surface area of ​​25.8 parts by weight is about 300m 2 / g of fumed silica filler. The silica is hydrophobized and has about 0.178 mmol / g of vinyl functional groups.

[0195] The values ​​given as parts by weight are not percentage values ​​and therefore do not necessarily add to 100.

[0196] Polymer 1: Polymer 1 is a vinyl dimethyl terminated polydimethylsiloxane having a viscosity of 53,000 mPa.s at 25°C as measured using a Brookfield TM The rotational viscometer was measured at 6 rpm.

[0197] Polymer 2: Polymer 2 is a vinyl terminated poly(dimethylsiloxane-co-methylvinylsiloxane) having a viscosity of 370 mPa.s at 25°C measured at 12 rpm using a Brookfield 1000 with a cone and plate arrangement with cone CP-52. TM Rotational viscometer measurement,

[0198] Crosslinker 1: Crosslinker 1 is trimethyl terminated polymethylhydrogendimethylsiloxane having a viscosity of 30 mPa.s at 25°C as measured using a Brookfield 1000 with cone and plate arrangement with cone CP-52. TM The rotational viscometer was measured at 12 rpm.

[0199] Release agent: The release agent is a hydroxydimethyl terminated polydimethylsiloxane having a viscosity of about 21 mPa.s at 25°C, which is measured using a Brookfield TM The rotational viscometer was measured at 12 rpm.

[0200] Cyclotetrasiloxane: Cyclotetrasiloxane is tetravinyl-tetramethyl-cyclotetrasiloxane

[0201] Phenyl Methyl Siloxane Copolymer: Phenyl Methyl Siloxane Copolymer is a trimethylsilyl terminated phenyl methyl siloxane dimethyl siloxane copolymer having a viscosity of 125 mPa.s at 25°C as measured using a Brookfield 1000 with cone and plate arrangement with cone CP-52. TM The rotational viscometer was measured at 12 rpm.

[0202] CDA 6: CDA 6 is dodecanedioyl-bis-(N'-salicyloyl)hydrazine, a synonym of which is 1-N',12-N'-bis(2-hydroxybenzoyl)dodecanedihydrazide, which is used as ADK STAB TM CDA-6 is commercially available from Adeka Corporation.

[0203] In use, the composition of part (A) and part (B) is mixed together in a 1: 1 weight ratio. The resulting composition is inserted into a suitable mold and cured at 175°C for a period of 10 minutes to a button-shaped object with a thickness of 12.5 mm and a diameter of 29 mm. Unless otherwise stated, the resulting silicone rubber is not post-cured. The post-cured sample is post-cured at 200°C for 4 hours. Unless otherwise stated, all subsequent compression set results are determined according to the International Organization for Standardization (ISO) test 815-1:2019 method A.

[0204] The compression set additive was added to the Elas.1 LSR composition of Table 1.

[0205] Compression at several alternative temperatures (compr n ) After a period of 22 hours, the compression set of the cured samples of Elas.1 was evaluated

[0206] Ref.1 provides the compression set values ​​produced when the composition of Elas.1 contains no compression set additive and is not post-cured. Ref.1+PC are the same samples as those in Ref.1, but wherein the samples are cured and then post-cured. Examples 1 and 2 and Comparative Examples 1 and 2 show the compression set results for elastomers produced from the Elas.1 composition, which contains 0.1 wt.% of the compression set additive.

[0207] After curing (and when post-curing is 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. After removal from the oven, the compression on each sample was released, allowed to cool for 30 minutes, and then the corresponding compression set value was determined. The results are provided in Table 2 below.

[0208] Table 2: Elas.1 samples compressed at different temperatures for 22 hours and analyzed according to ISO815-1:2019 Method A Deformation (CST) (%) .

[0209]

[0210] CDA 1 is 3-(n-salicyloyl)amino-1,2,4-triazole, a synonym of which is 2-hydroxy-N-1H-1,2,4-triazol-3-ylbenzamide, which is used as ADK STAB TM CDA-1 was commercially available from Adecco Corporation.

[0211] CS.1 is C–(CH2OC(=O)–CH2CH2–S-(C 12 H 25 ))4, pentaerythritol-tetrakis-(3-dodecyl-thio-propionate).

[0212] CS.2 is (C 12 H 25 )-OC(=O)-CH2CH2-S-CH2CH2-C(=O)-O-(C 12 H 25 ), 3,3'-dithiodipropionate.

[0213] The Ref.Elas.1 results for each temperature are actually the expected maximum compression set values ​​at each temperature after 22 hours of compression. The post-cured Elas.1 results are approximately the minimum compression set values ​​at the relevant temperature after 22 hours of compression, although longer post-curing times can further reduce the compression set values. The results using CS.1 and CS.2 provide excellent compression set values ​​after 22 hours of compression at all temperatures, while the commercially used compression set additives CDA-1 and CDA-6 have far less consistent initial compression across the temperature range.

[0214] Another series of tests was performed repeating the previous example at a different temperature, with the addition of 0.1 wt% of the compression set additive, but with compression maintained for 168 hours instead of 22 hours. The results are provided in Table 3 below.

[0215] Table 3: Elas.1 samples compressed at different temperatures for 168 hours and analyzed according to ISO 815-1:2019 Method A Shrinkage deformation (CST) (%) .

[0216]

[0217] To avoid when the theoretical maximum compression set is 100%, the compression set values ​​may be higher than 100%, as shown above in Table 2. Values ​​of 100% and higher indicate a complete loss of compression set and additional thermal shrinkage effects on the compression elastomer involved.

[0218] The Ex.3 and Ex.4 results, when compared to C.3 and C.4, had excellent compression set results after compression for 168 hours at temperatures below 200°C, but did not show stability in compression set at temperatures of 200°C and above (225°C). This indicates that the use of compression set additives CS.1 and CS.2 is generally better than CDA.1 and CDA.6 additives up to a compression temperature of about 190°C. This indicates that the compression set is improved when using CS.1 and CS.2 compared to CDA-1 and CDA-6 up to a temperature of about 190°C. Therefore, it is confirmed that the compound identified as component (e) is more consistently good with the compression set additive at temperatures from about 120°C to about 190°C.

[0219] It was found that the addition of at least one thiopropionate according to component (e) of the composition herein, i.e. CS.1 or CS.2, to the composition resulted in a significantly lower compression set of the resulting cured material after compression for 22 hours at up to 175° C. Compression set after compression at 200° C. was confirmed, but was relatively less significant.

[0220] Compression set additives were added to the Elas.2 LSR compositions of Table 1.

[0221] In a second series of examples, Ref. 2 is the compression set of the cured elastomer resulting from curing the Elas. 2 LSR composition as described in Table 1 in the absence of a compression set additive.

[0222] In Comparative Example 5, 0.1 wt % CDA-6 was added as a comparative compression set additive;

[0223] 0.2 wt% of CS-2 was added as a compression set additive in Ex. 5, resulting in Ex. 5 having only CS.2 as a compression set additive. The compression set results for different elastomers made from the determined compositions are depicted in Table 4 below.

[0224] Table 4: Addition of compression set additives to Elas.2 LSR compositions

[0225]

[0226] It can be seen that the presence of a release agent in Ex. 5 does not affect the effect of CS2 on the compression set results of Ex. 5 compared to CDA 6 after compression at 175°C for 22 hours. However, Ex. 5 gives worse results than C.5 (which relies on CDA 6) at a higher temperature of 200°C. This means that the compression set of the cured silicone elastomer of Ex. 5 is again greatly improved when at least one thiopropionate according to component (e) of the composition herein is used (i.e. CS.2 in this case, instead of CDA1 and CDA 6), after compression at up to 175°C for 22 hours.

[0227] The compression set additive CS.1 was added to the Elas.3 LSR composition of Table 1

[0228] In the third series of examples, a general purpose LSR, namely Elas.3, is used. When components A and B are mixed together, it contains 0.025 wt% CDA 6, with 0.05 wt% CDA 6 present in the part (B) composition before mixing. Therefore, Comparative Example 6 (C.6) tests the compression set of Elas.3 alone (containing 0.025 wt% CDA 6). In Ex.6, Elas.3 is evaluated, which has an additional 0.1 wt% CS.1. Therefore, Ex.6 contains 0.025 wt% CDA-6 and 0.1 wt% CS.1. The results are provided in Table 5 below.

[0229] Table 5: Compression set additives added to the Elas.3 LSR composition of Table 1 (initially containing 0.025 wt. % CDA 6)

[0230]

[0231] Ex.6 shows further improvement in compression set when CS.1 is added to the Elas.3 composition at a level of 0.1 wt% along with CDA 6. It can be seen that the addition of a small amount of tetra-dodecyl-thio-propionate significantly reduces the compression set of the cured product of the Elas.3 composition after compression at 175°C for 22 hours. The combination of CDA 6 and CS.1 also has a significant effect on compression set after compression at 200°C for 22 hours.

[0232] Addition of additional compression set additives to the Elas.3 LSR composition of Table 1

[0233] In another series of embodiments, a common type of LSR, namely Elas.3, is again used.

[0234] In Comparison 7 (C.7), the composition used was Elas.3 in combination with 0.3 wt% CDA 6 (ie, a total of 0.325 wt% CDA 6 in the composition when parts A and B were mixed together).

[0235] In Ex.7, the composition used was the same as C.7 together with 0.1 wt.% of CS.1; and in Ex.8, the composition used was the same as C.7 together with 0.3 wt.% of CS.1;

[0236] Table 6: Compression set additives added to the Elas.3 LSR composition of Table 1 (initially containing 0.025 wt. % CDA 6)

[0237]

[0238] Addition of higher amounts (compared to Tables 4 and 5) of CDA-6 and CS.1 was not found to further significantly improve compression set.

[0239] The data show that the addition of small amounts of 0.01-0.3 wt. % thio-(di)propionate significantly reduces the compression set after compression at temperatures up to about 190° C. for 22 hours.

[0240] Thus, it can be seen that the silicone elastomer material incorporating component (e) herein produces consistently good compression set results at temperatures up to about 190° C. without requiring a period of time for post-curing heating. Therefore, the silicone elastomer material is suitable for use in sealing parts requiring long-term heat resistance, such as when used as automotive sealing parts and sealing parts for electrical and electronic equipment.

Claims

1. A hydrosilylation-curable silicone rubber composition, comprising the following components: 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) organosilicon compounds having at least two, alternatively at least three Si—H groups per molecule; c) optionally hydrophobically treated silica reinforcing fillers; d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; e) at least one thiopropionate selected from the group consisting of R 1 -O-C(=O)-CH2CH2-S-CH2CH2-C(=O)-O-R 1 and C–(CH2OC(=O)–CH2CH2–S-R 1 )4 Each R 1 Can be the same or different and are alkyl groups, wherein the total weight % of the composition is 100 weight %.

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

4. The silicone rubber composition according to any preceding claim, wherein in the at least one thiopropionate of component (e), each R 1 is a straight chain alkyl group having 10 to 25 carbons.

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

6. A silicone rubber composition according to any preceding claim, wherein the composition is stored in two parts, part (A) and part (B) prior to use to keep components (b) and (d) separate to avoid premature curing.

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

8. The silicone rubber composition according to any preceding claim, further comprising one or more additives selected from the group consisting of cure inhibitors, blowing agents, mold release agents, adhesion catalysts, peroxides, electrically conductive fillers, thermally conductive fillers, pot life extenders, flame retardants, lubricants, heat stabilizers, UV light stabilizers, bactericides and / or wetting agents.

9. A silicone elastomeric material which is the cured product of the hydrosilylation-curable silicone rubber composition according to any preceding claim.

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

11. A method for preparing a silicone elastomer material, the method comprising the following steps: mixing the hydrosilylation-curable silicone rubber composition according to any one of claims 1 to 8; and curing the composition at a temperature of 80°C to 200°C.

12. A silicone elastomer material obtained or obtainable by a method comprising the following steps: mixing a hydrosilylation-curable silicone rubber composition according to any one of claims 1 to 8; and curing the composition at a temperature of 80°C, the silicone elastomer material having a compression set of 25% or less, preferably 20%, after compression for 22 hours at 175°C when measured according to industrial standard ISO 815-1:2019 method A, and / or having a compression set of 40% or less after compression for 168 hours at 175°C when measured according to industrial standard ISO 815-1:2019 method A.

13. Use of at least one thiopropionic acid ester selected from the following R 1 -O-C(=O)-CH2CH2-S-CH2CH2-C(=O)-O-R 1 and C–(CH2OC(=O)–CH2CH2–S-R 1 )4 Each R 1 may be the same or different and are alkyl groups; the use is as a means of reducing compression set in a silicone elastomer material, the silicone elastomer material being a cured product of a hydrosilylation-curable silicone rubber composition, the silicone rubber composition further comprising the following components: 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) organosilicon compounds having at least two, alternatively at least three Si—H groups per molecule; c) optionally hydrophobically treated silica reinforcing fillers; d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; The total weight % of the composition is 100 weight %.

14. Use of a silicone rubber composition according to any one of claims 1 to 8 in the manufacture of electrical, electronic and / or insulation applications, exterior waterproofing applications and / or equipment designed for drip irrigation / trickle irrigation applications.

15. Use according to claim 14, wherein the electrical, electronic and / or insulation applications may be selected from silicone coatings for non-silicone insulators, cable coatings for electrical connectors, terminals and wire seals, heat sink components for broadband cellular networks and communication electronics.

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